[CHORE] Fix the labeller CI step failing on main (#2142)

Splits our CI steps into two workflows:

1. `PR Labeller`: Autolabelling + (required) check that a label is
applied
2. `Release Drafter`: drafts a new release on push to `main`

This lets us better control permissioning (so that `PR Labeller` can be
run from forks, and won't have access to `contents: write` permissions)

---------

Co-authored-by: Jay Chia <[email protected]@users.noreply.github.com>

.github/workflows/pr-labeller.yml

@@ -0,0 +1,67 @@
+# Adapted from: https://github.com/release-drafter/release-drafter#readme
+
+name: PR Labeller
+
+on:
+  # pull_request event is required only for autolabeler
+  # pull_request:
+    # Only following types are handled by the action, but one can default to all as well
+    # types: [opened, reopened, synchronize, edited, labeled, unlabeled]
+  # pull_request_target event is required for autolabeler to support PRs from forks
+  pull_request_target:
+    branches: [main]
+    types: [opened, reopened, synchronize, edited, labeled, unlabeled]
+
+# write permission is required for autolabeler and commenting on the PR
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  run_auto_labeller:
+    runs-on: ubuntu-latest
+    steps:
+      # (Optional) GitHub Enterprise requires GHE_HOST variable set
+      #- name: Set GHE_HOST
+      #  run: |
+      #    echo "GHE_HOST=${GITHUB_SERVER_URL##https:\/\/}" >> $GITHUB_ENV
+
+      # Drafts your next Release notes as Pull Requests are merged into "master"
+    - uses: release-drafter/release-drafter@v6
+        # (Optional) specify config name to use, relative to .github/. Default: release-drafter.yml
+        # with:
+        #   config-name: my-config.yml
+        #   disable-autolabeler: true
+      with:
+        disable-releaser: true
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  # Check that at least one of the required labels was applied on this PR
+  label:
+    # Only run after the auto-labeller completes (in `run_auto_labeller`)
+    needs: run_auto_labeller
+    runs-on: ubuntu-latest
+    steps:
+    - uses: mheap/github-action-required-labels@v5
+      with:
+        mode: minimum
+        count: 1
+        labels: performance, enhancement, bug, chore, documentation, dependencies
+        add_comment: true
+        message: |
+          This PR is being prevented from merging because you need at least one of the required labels:
+
+          ```
+          enhancement | performance | bug | chore | documentation | dependencies
+          ```
+
+          The canonical and easiest way of adding them is to add the following prefixes to your PR title:
+
+          * [FEAT]: adds the `enhancement` label
+          * [PERF]: adds the `performance` label
+          * [BUG]: adds the `bug` label
+          * [CHORE]: adds the `chore` label
+          * [DOCS]: adds the `documentation` label
+
+          Thanks for helping us categorize and manage our PRs!

.github/workflows/release-drafter.yml

@@ -7,26 +7,16 @@ on:
     # branches to consider in the event; optional, defaults to all
     branches:
     - main
-  # pull_request event is required only for autolabeler
-  # pull_request:
-    # Only following types are handled by the action, but one can default to all as well
-    # types: [opened, reopened, synchronize, edited, labeled, unlabeled]
-  # pull_request_target event is required for autolabeler to support PRs from forks
-  pull_request_target:
-    branches: [main]
-    types: [opened, reopened, synchronize, edited, labeled, unlabeled]
 
 permissions:
-  contents: read
+  # write permission is required to create a github release
+  contents: write
+  # write permission is required for autolabeler (which we don't use here)
+  # otherwise, read permission is required at least
+  pull-requests: read
 
 jobs:
   update_release_draft:
-    permissions:
-      # write permission is required to create a github release
-      contents: write
-      # write permission is required for autolabeler
-      # otherwise, read permission is required at least
-      pull-requests: write
     runs-on: ubuntu-latest
     steps:
       # (Optional) GitHub Enterprise requires GHE_HOST variable set
@@ -42,35 +32,3 @@ jobs:
         #   disable-autolabeler: true
       env:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-
-  # Check that at least one of the required labels was applied on this PR
-  label:
-    # Only run on non-main jobs (pending PRs), and after the auto-labeller completes (in `update_release_draft`)
-    if: github.event.pull_request.head.ref != 'refs/heads/main'
-    needs: update_release_draft
-    runs-on: ubuntu-latest
-    permissions:
-      pull-requests: write
-    steps:
-    - uses: mheap/github-action-required-labels@v5
-      with:
-        mode: minimum
-        count: 1
-        labels: performance, enhancement, bug, chore, documentation, dependencies
-        add_comment: true
-        message: |
-          This PR is being prevented from merging because you need at least one of the required labels:
-
-          ```
-          enhancement | performance | bug | chore | documentation | dependencies
-          ```
-
-          The canonical and easiest way of adding them is to add the following prefixes to your PR title:
-
-          * [FEAT]: adds the `enhancement` label
-          * [PERF]: adds the `performance` label
-          * [BUG]: adds the `bug` label
-          * [CHORE]: adds the `chore` label
-          * [DOCS]: adds the `documentation` label
-
-          Thanks for helping us categorize and manage our PRs!