ci(renovate): Set rebaseWhen explicitly

Setting it to "conflicted", see
https://docs.renovatebot.com/configuration-options/#rebasewhen

Hopefully this will stop it from rebasing everytime a PR is merged.
Ref: #1416

Author: yedayak

.github/renovate.json

@@ -15,6 +15,7 @@
   ],
   "semanticCommits": "enabled",
   "commitMessageTopic": "{{depName}}",
+  "rebaseWhen": "conflicted",
   "dockerfile": {
     "enabled": false
   },