Find out flake rates for tests

[sentrivana]

Find out which tests are flaky so that we know what to look into. Find a good flake cutoff.

We might be able to use prevent for this: https://sentry.sentry.io/prevent/tests/?integratedOrgName=getsentry&preventPeriod=7d&repository=sentry-python

[linear]

PY-1975

[sentrivana]

According to Prevent we're at 0 flake rate in the last week, so I'll close this.