Change Maven cache key in GHA

Trying to invalidate a corrupted repository.

Author: acogoluegnes

.github/workflows/test-linux.yml

@@ -35,7 +35,7 @@ jobs:
         uses: actions/cache@v2
         with:
           path: ~/.m2
-          key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
+          key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}-v2
           restore-keys: ${{ runner.os }}-m2
       - name: Enable MQTT and STOMP plugins
         run: docker exec ${{job.services.rabbitmq.id}} rabbitmq-plugins enable rabbitmq_mqtt rabbitmq_stomp