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] <support@github.com>

Author: dependabot[bot]

.github/workflows/build.yml

@@ -32,7 +32,7 @@ jobs:
         run: |
           ./build-appimage.sh
       - name: Archive artifacts
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: AppImage
           path: MusicBrainz-Picard*.AppImage*
@@ -109,7 +109,7 @@ jobs:
           timestamp-rfc3161: http://timestamp.acs.microsoft.com
           timestamp-digest: SHA256
       - name: Archive artifacts
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: Windows
           path: source/dist/*.exe