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] <[email protected]>

Author: dependabot[bot]

.github/workflows/dotnet.yml

@@ -15,7 +15,7 @@ jobs:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Setup .NET
         uses: actions/setup-dotnet@v5
         with:
@@ -50,7 +50,7 @@ jobs:
     runs-on: ubuntu-latest
     needs: build
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Setup .NET
         uses: actions/setup-dotnet@v5
         with:
@@ -81,7 +81,7 @@ jobs:
     runs-on: ubuntu-latest
     needs: build
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Setup .NET
         uses: actions/setup-dotnet@v5
         with: