Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/add-issue-to-project.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
       - name: Checkout repository code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Add newly opened issue to GitHub Project
         uses: actions/add-to-project@v1.0.2

.github/workflows/ci.yaml

@@ -28,7 +28,7 @@ jobs:
             java: 25
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Set up JDK
       uses: actions/setup-java@v5
       with:

.github/workflows/main.yaml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: Set up JDK 17 and Maven settings for signing and publishing