[3.14] gh-141174: Improve `ForwardRef` test coverage (GH-141175) (#141354)

gh-141174: Improve `ForwardRef` test coverage (GH-141175)

* Test unsupported format in ForwardRef.evaluate()

* Test dict cell closure with multiple variables

* Test all options in ForwardRef repr

* Test ForwardRef being a final class
(cherry picked from commit 19b573025e0aa569e7a34081116280133e33979a)

Co-authored-by: dr-carlos <77367421+dr-carlos@users.noreply.github.com>