ci: Add meta job (#56)

.github/workflows/ci.yaml

@@ -88,3 +88,22 @@ jobs:
 
             -   name: Run tests
                 run: vendor/bin/phpunit --verbose --stop-on-failure
+
+    # This is a "trick", a meta task which does not change, and we can use in
+    # the protected branch rules as opposed to the individual tests which
+    # may change regularly.
+    validate-tests:
+        name: Tests status
+        runs-on: ubuntu-latest
+        needs:
+            - php-cs-fixer
+            - phpunit
+        if: always()
+        steps:
+            - name: Successful run
+              if: ${{ !(contains(needs.*.result, 'failure')) }}
+              run: exit 0
+
+            - name: Failing run
+              if: ${{ contains(needs.*.result, 'failure') }}
+              run: exit 1