Bump actions/upload-artifact from 5 to 6 in /.github/actions/build-vsix

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] <support@github.com>

Author: dependabot[bot]

.github/actions/build-vsix/action.yml

@@ -93,7 +93,7 @@ runs:
         VSIX_NAME: ${{ inputs.vsix_name }}
 
     - name: Upload VSIX
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       with:
         name: ${{ inputs.artifact_name }}
         path: ${{ inputs.vsix_name }}