Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/main.yml

@@ -7,7 +7,7 @@ jobs:
  matrix:
  java-version: [ 8, 11, 17, 21, 25 ]
  steps:
- - uses: actions/checkout@v5
+ - uses: actions/checkout@v6
 
  - uses: actions/setup-java@v5
  with: