Bump actions/upload-artifact from 5 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v5...v6)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  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/ci.yml

@@ -35,7 +35,7 @@ jobs:
       run: dotnet pack --configuration Release ValveKeyValue/ValveKeyValue/ValveKeyValue.csproj
 
     - name: Upload nupkg
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       if: matrix.os == 'ubuntu-latest'
       with:
         name: nupkg