[CI] Add coq-check-all job (#416)

This allows branch protection (for automerge) that doesn't need to
evolve as tested Coq versions change

.github/workflows/coq.yml

@@ -67,3 +67,13 @@ jobs:
         submodules: recursive
     - name: make
       run: TIMED=1 make
+
+  coq-check-all:
+    runs-on: ubuntu-latest
+    needs: build
+    if: always()
+    steps:
+    - run: echo 'build passed'
+      if: ${{ needs.build.result == 'success' }}
+    - run: echo 'build failed' && false
+      if: ${{ needs.build.result != 'success' }}