Bump actions/checkout from 3 to 6 in the dotnet group

Bumps the dotnet group with 1 update: [actions/checkout](https://github.com/actions/checkout).


Updates `actions/checkout` from 3 to 6
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v6)

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

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

Author: dependabot[bot]

.github/workflows/mirror-to-ado.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout GitHub repo
-        uses: actions/checkout@v3
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0