Move CI to Gitea Actions

The repository is hosted on Gitea, so the workflow moves to
.gitea/workflows/. actions/upload-artifact is pinned to v3 because
Gitea Actions does not support v4.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -49,7 +49,7 @@ jobs:
           cd "$smoke"
           "$smoke/venv/bin/openhop-influxdb" --version
           OPENHOP_PLUGIN_DATA="$smoke/data" "$smoke/venv/bin/openhop-influxdb" --check-config
-      - uses: actions/upload-artifact@v4
+      - uses: actions/upload-artifact@v3  # Gitea Actions does not support v4
         if: matrix.python-version == '3.11'
         with:
           name: wheel