chore(deps): update dependency open-policy-agent/regal to v0.42.0

Replace matchNewValue with allowedVersions constraint to properly
prevent Renovate from creating update branches for major versions.
The previous enabled/matchNewValue approach did not prevent branch
creation for already existing PRs.

renovate.json

@@ -6,9 +6,8 @@
   ],
   "packageRules": [
     {
-      "enabled": false,
-      "matchPackageNames": ["open-policy-agent/regal"],
-      "matchNewValue": "^2"
+      "allowedVersions": "<1.0.0",
+      "matchPackageNames": ["open-policy-agent/regal"]
     }
   ]
 }