Bump actions/upload-artifact from 3 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 3 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v3...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] <[email protected]>

Author: dependabot[bot]

.github/workflows/build.yml

@@ -39,13 +39,13 @@ jobs:
         run: flutter build web --release
 
       - name: Upload APK
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v6
         with:
           name: apk
           path: build/app/outputs/flutter-apk/app-release.apk
 
       - name: Upload Web
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v6
         with:
           name: web
           path: build/web/