chore : ci.yml jdk17 -> 21 변경

Author: ggamnunq

.github/workflows/ci.yml

@@ -20,11 +20,11 @@ jobs:
       - name: Checkout Code
         uses: actions/checkout@v3
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v3
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
 
       - name: Build Spring Boot Jar
         run: ./gradlew clean build -x test