Downgrade the JDK to 8 to be consistent with the JVM toolchain version and fix the Gradle build failure

Author: ShreckYe

.github/workflows/ci.yml

@@ -18,10 +18,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
-    - name: Set up JDK 21
+    - name: Set up JDK 8
       uses: actions/setup-java@v4
       with:
-        java-version: '21'
+        java-version: '8'
         distribution: 'temurin'
 
     - name: Setup Gradle
@@ -41,10 +41,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
-    - name: Set up JDK 21
+    - name: Set up JDK 8
       uses: actions/setup-java@v4
       with:
-        java-version: '21'
+        java-version: '8'
         distribution: 'temurin'
 
     - name: Generate and submit dependency graph