[3.12] gh-114763: Protect lazy loading modules from attribute access races (GH-114781) (GH-115870)

gh-114763: Protect lazy loading modules from attribute access races (GH-114781)

Setting the __class__ attribute of a lazy-loading module to ModuleType enables other threads to attempt to access attributes before the loading is complete. Now that is protected by a lock.
(cherry picked from commit 200271c61db44d90759f8a8934949aefd72d5724)

Co-authored-by: Chris Markiewicz <effigies@gmail.com>