build(deps): bump actions/download-artifact from 7 to 8 (#501)

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 7 to 8.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v7...v8)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '8'
  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>

Author: dependabot[bot]

.github/workflows/update-flathub-sources.yml

@@ -187,7 +187,7 @@ jobs:
         fetch-depth: 0
 
     - name: Download generated-sources.json artifact
-      uses: actions/download-artifact@v7
+      uses: actions/download-artifact@v8
       with:
         name: generated-sources-json
         path: ./