Update GitHub Actions checkout action version

Author: pgleeson

.github/workflows/ci.yml

@@ -29,7 +29,7 @@ jobs:
 
     name: Test on Java ${{ matrix.Java }} on ${{ matrix.runs-on }}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Set up JDK ${{ matrix.Java }}
       uses: actions/setup-java@v4
       with: