refactor: replace deprecated user property rules with enforcer.rules

The Maven Enforcer Plugin replaced the rules property with the enforcer.rules property. See issue
for additional details.

Fixes #56

templates/gitlab-ci-maven.yml

@@ -702,7 +702,7 @@ mvn-no-snapshot-deps:
   stage: test
   needs: []
   script:
-    - mvn ${TRACE:+-X} $MAVEN_CLI_OPTS $mvn_settings_opt $java_proxy_args enforcer:enforce -Drules=requireReleaseDeps
+    - mvn ${TRACE:+-X} $MAVEN_CLI_OPTS $mvn_settings_opt $java_proxy_args enforcer:enforce -Denforcer.rules=requireReleaseDeps
   rules:
     # exclude if disabled
     - if: '$MVN_FORBID_SNAPSHOT_DEPENDENCIES_DISABLED == "true"'