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
...

See gh-1730

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

Author: dependabot[bot]

.github/workflows/build-pull-request.yml

@@ -11,7 +11,7 @@ jobs:
     if: ${{ github.repository == 'spring-io/initializr' }}
     steps:
       - name: Check out
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Set up JDK 17
         uses: actions/setup-java@v5

.github/workflows/build.yml

@@ -27,7 +27,7 @@ jobs:
     runs-on: ${{ matrix.runner.os }}
     steps:
       - name: Check out
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Set up JDK 17
         uses: actions/setup-java@v5

.github/workflows/release.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Set up JDK 17
         uses: actions/setup-java@v5
         with:
@@ -52,7 +52,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Sync to Maven Central
         uses: ./.github/actions/sync-to-maven-central
         with:
@@ -83,7 +83,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Create GitHub Release
         uses: ./.github/actions/create-github-release
         with: