Add `Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST` and
`Py_END_CRITICAL_SECTION_SEQUENCE_FAST` macros and update `str.join` to use
them. Also add a regression test that would crash reliably without this
patch.
(cherry picked from commit baf347d916)
Co-authored-by: Josh {*()} Rosenberg <26495692+MojoVampire@users.noreply.github.com>