Markup other dependencies in Dockerfile for Renovate (#3945)

renovate.json5

@@ -11,5 +11,6 @@
         "# renovate: datasource=(?<datasource>[a-z-]+?)(?: packageName=(?<packageName>.+?))?(?: versioning=(?<versioning>[a-z-]+))?\\s(?:ENV|ARG) .+?_VERSION=(?<currentValue>.+?)\\s"
       ]
     }
-  ]
+  ],
+  "labels": ["dependencies"]
 }