Update gradle.yml

Author: jwnnoh

.github/workflows/gradle.yml

@@ -19,7 +19,7 @@ jobs:
     - name: main 브랜치로 이동
       uses: actions/checkout@v3
       with:
-        ref: production
+        ref: main
     - name: JDK 11 설치
       uses: actions/setup-java@v3
       with: