Update type hint for the CancelStatus.parent setter

[A5rocks]

Type hint issue spotted in python/mypy#18510

Maybe we should wait for that to be merged (and maybe released?) to check this works.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00000%. Comparing base (ed2a7d3) to head (d11481b).
Report is 48 commits behind head on main.

Additional details and impacted files

@@               Coverage Diff               @@
##                 main        #3191   +/-   ##
===============================================
  Coverage   100.00000%   100.00000%           
===============================================
  Files             124          124           
  Lines           18460        18460           
  Branches         1216         1216           
===============================================
  Hits            18460        18460           

Files with missing lines	Coverage Δ
src/trio/_core/_run.py	100.00000% <100.00000%> (ø)

[TeamSpen210]

Before that PR setter hints were effectively ignored (aside from property implementation), so it should be fine. Could just install the PR code locally to check.

[CoolCat467]

Looks simple enough, don't see any reason why this wouldn't be mergeable at this time even though the mypy PR hasn't gone through yet.