Update Java version in workflow to 21

Author: lemire

.github/workflows/basic.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        java: [ 17, 21 ]
+        java: [ 21 ]
     steps:
       - uses: actions/[email protected]
       - name: Set up JDK