[3.13] gh-121025: Improve partialmethod.__repr__ (GH-121033) (#121037)

gh-121025: Improve partialmethod.__repr__ (GH-121033)

It no longer contains redundant commas and spaces.
(cherry picked from commit d2646e3f45e3e4e831ee2ae84d55b161a361d592)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>