style: change default input value syntax (equivalent)

templates/gitlab-ci-maven.yml

@@ -27,7 +27,7 @@ spec:
       default: .m2
     settings-file:
       description: The Maven `settings.xml` file path
-      default: ${MAVEN_CFG_DIR}/settings.xml
+      default: $MAVEN_CFG_DIR/settings.xml
     opts:
       description: '[Global Maven options](http://maven.apache.org/configure.html#maven_opts-environment-variable)'
       default: >-