flask: fix tests
flask: fix tests

Flask 2.2 has compatibility issues with pytest-asyncio (https://github.com/pallets/flask/issues/4773),
but it turns out we don't even need our tests to be async here. So we just use sync tests to fix the CI issues.

mitmproxy/mitmproxy,mhils/mitmproxy,mhils/mitmproxy,mhils/mitmproxy,mitmproxy/mitmproxy,mitmproxy/mitmproxy,mitmproxy/mitmproxy,mitmproxy/mitmproxy,mhils/mitmproxy,mhils/mitmproxy