chore: bump @actions/github to 9.1.0 for release

- Version bump 9.0.0 → 9.1.0 in package.json
- Update RELEASES.md with idempotency guard note and PR link

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "@actions/github",
-  "version": "9.0.0",
+  "version": "9.1.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@actions/github",
-      "version": "9.0.0",
+      "version": "9.1.0",
       "license": "MIT",
       "dependencies": {
         "@actions/http-client": "^3.0.2",