Update gradle.yml

Author: JangDongHo

.github/workflows/gradle.yml

@@ -15,7 +15,7 @@ on:
 
 jobs:
   build:
-    if: github.event.pull_request.head.repo.full_name == github.repository
+    if: github.event.repository.fork == false
     runs-on: ubuntu-latest
     permissions:
       id-token: write