[3.15] gh-151722: Do not track the frozendict in the GC in _PyDict_FromKeys() (GH...

[3.15] gh-151722: Do not track the frozendict in the GC in _PyDict_FromKeys() (GH-152067) (#152225)

gh-151722: Do not track the frozendict in the GC in _PyDict_FromKeys() (GH-152067)

_PyDict_FromKeys() now creates a frozendict copy which is
not tracked by the GC.

dict_merge() no longer requires the dictionary to be tracked by the
GC.
(cherry picked from commit 55bc3126e0a09a8e940da73e51ab1ffeecaf02d4)

Co-authored-by: Victor Stinner <vstinner@python.org>
Co-authored-by: Donghee Na <donghee.na@python.org>
Co-authored-by: Inada Naoki <songofacandy@gmail.com>