fix(renovate): do not post status checks (#3)

The GitHub App reads statuses but cannot write them. Renovate posts a
renovate/stability-days status on each branch for minimumReleaseAge. The
403 aborted the run as "repository changed" right after the first
branch was created. Turn the Renovate status checks off. minimumReleaseAge
still holds a release back.

renovate.json

@@ -65,5 +65,11 @@
         "major"
       ]
     }
-  ]
+  ],
+  "statusCheckNames": {
+    "artifactError": null,
+    "configValidation": null,
+    "mergeConfidence": null,
+    "minimumReleaseAge": null
+  }
 }