GitHub Actions: Downgrade maven workflow to 11.0.16+8

Author: bantu

.github/workflows/maven.yml

@@ -19,7 +19,9 @@ jobs:
     - name: Set up JDK 11
       uses: actions/setup-java@v2
       with:
-        java-version: '11'
+        # TODO: Revert to '11'.
+        # See https://github.com/ChargeTimeEU/Java-OCA-OCPP/pull/223#issuecomment-1328048028
+        java-version: '11.0.16+8'
         distribution: 'temurin'
         cache: maven
     - name: Build with Maven