ci: bump actions/upload-artifact from 5 to 6 in /.github/workflows

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/ci.yml

@@ -128,7 +128,7 @@ jobs:
         fi
 
     - name: Upload build artifacts
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       with:
         name: stackaroo-${{ matrix.goos }}-${{ matrix.goarch }}
         path: stackaroo-*

.github/workflows/release.yml

@@ -144,7 +144,7 @@ jobs:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
     - name: Upload release artifacts
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       if: always()
       with:
         name: release-artifacts