Use JDK 21 to execute Gradle

Gradle 9.x expects JVM 17 or above. Use a similar env as NewPipe so that Gradle works without issues.

Signed-off-by: Aayush Gupta <aayushgupta219@gmail.com>

Author: theimpulson

.github/workflows/ci.yml

@@ -27,10 +27,10 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
-      - name: set up JDK 11
+      - name: set up JDK 21
         uses: actions/setup-java@v5
         with:
-          java-version: '11'
+          java-version: 21
           distribution: 'temurin'
 
       - name: Cache Gradle wrapper dists

.github/workflows/docs.yml

@@ -15,10 +15,10 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
-      - name: set up JDK 11
+      - name: set up JDK 21
         uses: actions/setup-java@v5
         with:
-          java-version: '11'
+          java-version: 21
           distribution: 'temurin'
 
       - name: Cache Gradle dependencies