Fix Gradle workflows to setup JDK 21

Author: 2008Choco

.github/workflows/gradle_build.yml

@@ -12,10 +12,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
-    - name: Set up JDK 17
+    - name: Set up JDK 21
       uses: actions/setup-java@v4
       with:
-        java-version: 17
+        java-version: 21
         distribution: 'temurin'
     - name: Grant execute permission for gradlew
       run: chmod +x gradlew

.github/workflows/gradle_publish.yml

@@ -10,10 +10,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
-    - name: Set up JDK 17
+    - name: Set up JDK 21
       uses: actions/setup-java@v4
       with:
-        java-version: 17
+        java-version: 21
         distribution: 'temurin'
     - name: Grant execute permission for gradlew
       run: chmod +x gradlew