Update CI configuration

- also test against GAP 4.12
- update to latest versions for various actions
- error out if documentation job failed to produce a PDF

.github/workflows/CI.yml

@@ -25,12 +25,13 @@ jobs:
       matrix:
         gap-branch:
           - master
+          - stable-4.12
           - stable-4.11
           - stable-4.10
           - stable-4.9
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: 'Install additional dependencies'
         run: |
           sudo apt-get update
@@ -41,15 +42,15 @@ jobs:
       - uses: gap-actions/build-pkg@v1
       - uses: gap-actions/run-pkg-tests@v2
       - uses: gap-actions/process-coverage@v2
-      - uses: codecov/codecov-action@v2
+      - uses: codecov/codecov-action@v3
 
   # The documentation job
   manual:
     name: Build manuals
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: 'Install additional dependencies'
         run: |
           sudo apt-get update
@@ -59,7 +60,8 @@ jobs:
         with:
           use-latex: 'true'
       - name: 'Upload documentation'
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v3
         with:
           name: manual
           path: ./doc/manual.pdf
+          if-no-files-found: error