run tests with java 21
diff --git a/.github/workflows/gradle-precommit.yml b/.github/workflows/gradle-precommit.yml
index c6b5dfe..0e3c2d6 100644
--- a/.github/workflows/gradle-precommit.yml
+++ b/.github/workflows/gradle-precommit.yml
@@ -59,7 +59,7 @@
         # macos-latest: a tad slower than ubuntu and pretty much the same (?) so leaving out.
         os: [ubuntu-latest]
         # Test JVMs.
-        java: [ '17' ]
+        java: [ '21' ]
 
     env:
       GRADLE_ENTERPRISE_ACCESS_KEY: ${{ secrets.GE_ACCESS_TOKEN }}