Supports building with Java 21

Author: yidongnan

.github/workflows/build-master.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        java: ['17']
+        java: ['17', '21']
     steps:
       - name: Checkout code
         uses: actions/checkout@v4

.github/workflows/pull-request.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        java: ['17']
+        java: ['17', '21']
     steps:
       - name: Checkout code
         uses: actions/checkout@v4