gha: limit nixos builds to master and manual

Running these on every PR or every push to a PR quickly gets us
rate limited by github. Its unclear if theres a way around this cache
rate limit:
https://github.com/DeterminateSystems/magic-nix-cache-action?tab=readme-ov-file#usage-notes

Moving this to only running on `master` and manually should do the trick
for now. If it persists we might have to move it to a scheduled job like
openwrt builds.

.github/workflows/ci-nixos.yml

@@ -0,0 +1,40 @@
+name: ci-nixos
+on:
+  push: # This is only run when PRs are merged into master
+    branches:
+      - master
+  workflow_dispatch:
+# These jobs can take a long time and potentially cause us to bump up against CI
+# rate limits. Instead we've opted to run these only on merges to master. We might
+# have to limit these further if the rate limiting remains
+jobs:
+  nixos_configs_get:
+    name: nixos configurations get name
+    runs-on: ubuntu-latest
+    outputs:
+      nixosconfignames: ${{ steps.nixosconfigsget.outputs.nixosconfignames }}
+    steps:
+      - uses: actions/checkout@v3
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+      - name: Get all NixOS configurations
+        id: nixosconfigsget
+        run: |
+          nixosconfignames=$(nix eval .\#nixosConfigurations --apply builtins.attrNames --json)
+          echo "$nixosconfignames"
+          echo "nixosconfignames=$nixosconfignames" >> $GITHUB_OUTPUT
+  nixos_configs_build:
+    name: build ${{ matrix.configName }} nixos configuration
+    needs: nixos_configs_get
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        configName: ${{ fromJSON(needs.nixos_configs_get.outputs.nixosconfignames) }}
+    steps:
+      - uses: actions/checkout@v3
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+      - name: Build ${{ matrix.configName }} nixos configuration
+        run: |
+          nix build -L .#nixosConfigurations.${{ matrix.configName }}.config.system.build.toplevel

.github/workflows/ci.yml

@@ -28,33 +28,3 @@ jobs:
       - run: nix build -L .#massflash
       - run: nix build -L .#scaleInventory
       - run: nix build -L .#serverspec
-  nixos_configs_get:
-    name: nixos configurations get name
-    runs-on: ubuntu-latest
-    outputs:
-      nixosconfignames: ${{ steps.nixosconfigsget.outputs.nixosconfignames }}
-    steps:
-      - uses: actions/checkout@v3
-      - uses: DeterminateSystems/nix-installer-action@main
-      - uses: DeterminateSystems/magic-nix-cache-action@main
-      - name: Get all NixOS configurations
-        id: nixosconfigsget
-        run: |
-          nixosconfignames=$(nix eval .\#nixosConfigurations --apply builtins.attrNames --json)
-          echo "$nixosconfignames"
-          echo "nixosconfignames=$nixosconfignames" >> $GITHUB_OUTPUT
-  nixos_configs_build:
-    name: build ${{ matrix.configName }} nixos configuration
-    needs: nixos_configs_get
-    runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
-      matrix:
-        configName: ${{ fromJSON(needs.nixos_configs_get.outputs.nixosconfignames) }}
-    steps:
-      - uses: actions/checkout@v3
-      - uses: DeterminateSystems/nix-installer-action@main
-      - uses: DeterminateSystems/magic-nix-cache-action@main
-      - name: Build ${{ matrix.configName }} nixos configuration
-        run: |
-          nix build -L .#nixosConfigurations.${{ matrix.configName }}.config.system.build.toplevel