Bump actions/setup-dotnet from 5 to 6 (#11767)

Bumps [actions/setup-dotnet](https://github.com/actions/setup-dotnet) from 5 to 6.
- [Release notes](https://github.com/actions/setup-dotnet/releases)
- [Commits](https://github.com/actions/setup-dotnet/compare/v5...v6)

---
updated-dependencies:
- dependency-name: actions/setup-dotnet
  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>

.github/workflows/docx-validation.yaml

@@ -41,7 +41,7 @@ jobs:
 
     steps:
     - name: ensure dotnet is present
-      uses: actions/setup-dotnet@v5
+      uses: actions/setup-dotnet@v6
         
     - name: Install json_reformat
       run: |