Investigate flaky gevent test

[ericapisani]

Multiple times a day, a specific gevent test fails with the error assert 0 > 0 + where 0 = len([]).

This happens most frequently for Python 3.6, but this has been observed in v3.10 as well.

Investigate what the cause might be and see what's required to make these reliable

[linear-code]

PY-2127