If the flaky plugin for pytest is available, use its decorator to
support re-running unstable tests. In case the package is missing,
execute the test as usual without attempts to re-run it in case of
failure.
This is mostly intended to increase the test stability in CI. Using a
custom decorator enables us to keep the flaky package as an optional
dependency.
(cherry picked from commit 5b703de733)
f84e0f4ad0