build: prevent minor version upgrade of groovy-all dependency

Limit renovate to upgrading the groovy-all dependency to 2.5.x which is used
by hale»studio.

SVC-1398

renovate.json

@@ -2,5 +2,11 @@
     "$schema": "https://docs.renovatebot.com/renovate-schema.json",
     "extends": [
         "config:recommended"
+    ],
+    "packageRules": [
+          {
+            "matchPackageNames": ["org.codehaus.groovy:groovy-all"],
+            "allowedVersions": "<2.6.0"
+          }
     ]
 }