[3.15] Add tests for syntax error messages that had no test coverage (GH-153192)...

[3.15] Add tests for syntax error messages that had no test coverage (GH-153192) (GH-153196)

Add tests for syntax error messages that had no test coverage (GH-153192)

"illegal target for annotation" and "cannot use dict unpacking here"
were not tested at all, and "f-string: expecting '!', or ':', or '}'"
was only tested for its t-string variant.
(cherry picked from commit 836b2069c86e25cf9456e9210bb612e5166d0779)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>