Investigate and fix io_uring HTTP/3 tests

[vietj]

Version

5.2.0

Context

Http3ServerTest and Http3ClientTest hang often in CI when running io_uring transport.

Those tests have been disabled for now to improve the CI.

They should be investigated and fixed.

Steps to reproduce

1. fork this repository
2. remove the assume condition in Http3ServerTest and Http3ClientTest
3. make a PR on the repository fork
4. try to observe the test hanging in the io_uring profile, re-run actions if needed