use generic rule

Dockerfile

@@ -7,8 +7,11 @@ ENV XK6_SQL_DRIVER_POSTGRES_VERSION="0.1.0"
 ENV XK6_SQL_DRIVER_MYSQL_VERSION="0.1.0"
 ENV XK6_SQL_VERSION="1.0.1"
 ENV XK6_LOKI_VERSION="1.0.0"
+
+# renovate: datasource=github-releases depName=grafana/xk6
 ENV XK6_BUILDER_VERSION="0.14.2"
 
+
 RUN go install go.k6.io/xk6/cmd/xk6@v${XK6_BUILDER_VERSION}
 RUN xk6 build --output /k6 \
     --with github.com/GhMartingit/xk6-mongo@v${XK6_MONGO_VERSION} \

renovate.json5

@@ -107,6 +107,18 @@
       "datasourceTemplate": "github-releases",
       "versioningTemplate": "regex:v?(?<major>\\d+)\\.(?<minor>\\d+)\\.(?<patch>\\d+)?(?<prerelease>-[0-9A-Za-z-\\.]+)?$"
     }
+  ],
+  customManagers: [
+    {
+      customType: 'regex',
+      fileMatch: ["Dockerfile$"],
+      "matchStrings": [
+        // For dockerfile: https://regex101.com/r/iJfnnL/1
+        "datasource=(?<datasource>github-releases) depName=(?<depName>[\\w\\d\\//\\-\\_]+)\\nENV .+_VERSION[\\s*|=]??\\\"?(?<currentValue>[\\w\\d\\/\\-\\.\\_]+)\\\"?\\s*",
+      ],
+      // datasourceTemplate: "{{datasource}}", // should not be required as we extract datasource
+      versioningTemplate: "regex:(?<major>\\d+)\\.(?<minor>\\d+)\\.(?<patch>\\d+)?$",
+      extractVersionTemplate: "^v?(?<version>.*)$"
+    }
   ]
-
 }