Collect test matrix result into single job result (#3552)

.github/workflows/ci.yml

@@ -6,7 +6,22 @@ env:
   RUSTDOCFLAGS: "-Dwarnings"
 
 jobs:
+  # This allows us to have one branch protection rule for the full test matrix.
+  # See: https://github.com/orgs/community/discussions/4324
   tests:
+    name: Tests
+    runs-on: ubuntu-latest
+    needs: [test-matrix]
+    if: always()
+    steps:
+      - name: Tests successful
+        if: ${{ !(contains(needs.*.result, 'failure')) }}
+        run: exit 0
+      - name: Tests failing
+        if: ${{ contains(needs.*.result, 'failure') }}
+        run: exit 1
+
+  test-matrix:
     name: Tests
     strategy:
       matrix: