Bump actions/checkout from 5 to 6 (spiffe#370)

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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Max Lambrecht <maxlambrecht@gmail.com>

Author: dependabot[bot]

.github/workflows/build.yml

@@ -20,7 +20,7 @@ jobs:
         java-version: [ 8, 11, 17, 21 ]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up JDK
         uses: actions/setup-java@v5
         with:
@@ -54,7 +54,7 @@ jobs:
         java-version: [ 8, 11, 17, 21 ]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up JDK
         uses: actions/setup-java@v5
         with:

.github/workflows/coverage.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up JDK
         uses: actions/setup-java@v5
         with:

.github/workflows/java-spiffe-helper-ci.yaml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Setup QEMU
         uses: docker/setup-qemu-action@v3
       - name: Setup buildx

.github/workflows/release_build.yml

@@ -19,7 +19,7 @@ jobs:
       PGP_KEY_PASSPHRASE: ${{ secrets.PGP_KEY_PASSPHRASE }}
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Set up JDK
         uses: actions/setup-java@v5
         with:
@@ -35,7 +35,7 @@ jobs:
       contents: read
       packages: write
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Login to GitHub Container Registry
         uses: docker/login-action@v3
         with: