Force altool for macOS TestFlight upload

Author: prof18

.github/workflows/macos-testflight-release.yml

@@ -141,6 +141,7 @@ jobs:
       - uses: Apple-Actions/upload-testflight-build@v5
         with:
           app-type: 'osx'
+          backend: 'altool'
           app-path: ${{ env.RELEASE_PATH }}
           issuer-id: ${{ secrets.APPSTORE_ISSUER_ID }}
           api-key-id: ${{ secrets.APPSTORE_KEY_ID }}