[3.12] gh-104683: Rename Lib/test/clinic.test as Lib/test/clinic.test.c (GH-106443) (#106444)

gh-104683: Rename Lib/test/clinic.test as Lib/test/clinic.test.c (GH-106443)
(cherry picked from commit a941bd6c53ac4646926292557a7bb2a86f8025c3)

Co-authored-by: Erlend E. Aasland <erlend@python.org>