Update maven.yml

Author: wjglerum

.github/workflows/maven.yml

@@ -40,3 +40,12 @@ jobs:
     - name: Test with Maven
       run: ./mvnw -B verify --file pom.xml
       working-directory: ${{env.EXERCISES_DIRECTORY}}/${{matrix.exercise}}
+  summary:
+    if: ${{ always() }}
+    runs-on: ubuntu-latest
+    name: Build (matrix)
+    needs: build
+    steps:
+      - name: Check build matrix status
+        if: ${{ needs.build.result != 'success' }}
+        run: exit 1