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](https://github.com/actions/upload-artifact/compare/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>

.github/workflows/build.yml

@@ -36,7 +36,7 @@ jobs:
     - name: Build executable
       run: sbt executable
     - name: Upload artifacts
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       with:
         name: gitbucket-java${{ matrix.java }}-${{ github.sha }}
         path: ./target/executable/gitbucket.*