[3.14] gh-141174: Improve annotationlib._Stringifier test coverage (GH-141220)

[miss-islington]

• Test _Stringifier.__convert_to_ast() for containers

• Test partial evaluation of ForwardRefs in _Stringifier
  (cherry picked from commit 55ea132)

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

• Issue: annotationlib: Improve test coverage #141174

[dr-carlos]

Not sure why this PR is failing iOS builds? The error is

xcodebuild: error: Unable to find a device matching the provided destination specifier:
  		{ platform:iOS Simulator, OS:18.5, name:iPhone 16e }
  
  	The requested device could not be found because no available devices matched the request.

Which seems entirely unrelated to this PR - probably either a GitHub Actions issue or it just needs a re-run.

[JelleZijlstra]

Yeah I am retrying it.

[mhsmith]

@freakboy3742: Is this the same as actions/runner-images#12777? The error message looks different.

[freakboy3742]

@mhsmith There's 2 variants on the runner failure - "Simulator doesn't start", and "Simulator doesn't appear to exist at all". This looks like an example of the second type of error.

I logged actions/runner-images#13228 as a separate report; GitHub has closed that issue as duplicate of 12777. They seem to be hanging all hope on the 26.1 or 26.2 macOS release fixing all the problems they're seeing.