[3.13] gh-122798: Make tests for warnings in the re module more strict (GH-122799) (#122804)

gh-122798: Make tests for warnings in the re module more strict (GH-122799)

* Test warning messages.
* Test stack level for re.compile() and re.findall().
(cherry picked from commit d2e5be1f39bc3d48c7bc8c146c4bcadee266672a)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>