[3.12] gh-126543: Docs: change "bound type var" to "bounded" when used in the context of the 'bound' kw argument to TypeVar (GH-126584) (#126658)

(cherry picked from commit 434b29767f2fdef9f35c8e93303cf6aca4a66a80)

Co-authored-by: Pedro Fonini <fonini@protonmail.ch>