Add a header check to the CI Fix rucio#4980

The `add_header` script needs to be run after an edit to determine the status of
the header and, if necessary, change the header.

This commit adds the check for the header to the CI/CD. This enforces the usage
of the `add_header` script and ensures a healthy code base.

.github/workflows/autotest.yml

@@ -5,7 +5,22 @@ on:
   - push
 
 jobs:
+  add_header_test:
+    if: 'github.event_name == ''pull_request'''
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - run: |
+          for file in $(find . -type f -name '*.py')
+          do
+            tools/add_header --disable-add-me -cd -- $file
+          done
+          tools/add_header --disable-add-me -cd -- bin/*
   setup:
+    if: ${{ success() || cancelled() }}
+    needs: add_header_test
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2