Run CI on ubuntu-latest (#1576)

Ubuntu 20 image is closing down
https://github.blog/changelog/2024-12-05-notice-of-upcoming-releases-and-breaking-changes-for-github-actions/#ubuntu-20-image-is-closing-down

.github/workflows/deploy.yaml

@@ -10,7 +10,7 @@ jobs:
   # The l3build job contains the actual work. This is mostly the same as in main.yaml
   # and should stay synchronized. Sadly it doesn't seem possible to reuse the instructions at the moment.
   release:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     name: Build release
     environment: Release
     steps:

.github/workflows/main.yaml

@@ -15,7 +15,7 @@ on:
 jobs:
   # Update the TeX Live tree if necessary
   texlive-cache:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     name: Update TeX Live
     outputs:
       cache_key: ${{ steps.texlive.outputs.cache_key }}
@@ -34,7 +34,7 @@ jobs:
   # create three jobs which only differ in minimal elements.
   # For tags we do not run this since we run the release job instead.
   l3build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         # include indicates that we want to set explicitly these combinations
@@ -166,7 +166,7 @@ jobs:
           # Decide how long to keep the test output artifact:
           retention-days: 3
   docs:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         include:
@@ -215,7 +215,7 @@ jobs:
   # test failures.
   notifiy:
     name: Send notifications
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     # Run after the `l3build` job in order to be able to react to it's output.
     needs:
       - l3build

.github/workflows/pretest.yaml

@@ -7,7 +7,7 @@ on:
 jobs:
   # Update the TeX Live tree if necessary
   texlive-cache:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     name: Update TeX Live
     outputs:
       cache_key: ${{ steps.texlive.outputs.cache_key }}
@@ -28,7 +28,7 @@ jobs:
   # create three jobs which only differ in minimal elements.
   # For tags we do not run this since we run the release job instead.
   l3build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         # include indicates that we want to set explicitly these combinations
@@ -139,7 +139,7 @@ jobs:
           # Decide how long to keep the test output artifact:
           retention-days: 3
   docs:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         include: