Use as_() for correct type inference

[dlech]

as_() has replaced _from() for "casting" WinRT objects to different types.

I just did this in the web editor, so I haven't tested it, but it should avoid the type error that was being ignored.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.06%. Comparing base (26c6af2) to head (8f82691).
Report is 39 commits behind head on main.

Files with missing lines	Patch %	Lines
src/desktop_notifier/backends/winrt.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #219      +/-   ##
==========================================
- Coverage   85.13%   85.06%   -0.08%     
==========================================
  Files          10       10              
  Lines         895      951      +56     
==========================================
+ Hits          762      809      +47     
- Misses        133      142       +9     

Flag	Coverage Δ
pytest	85.06% <0.00%> (-0.08%)	⬇️

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[samschott]

Thanks! All tests pass, including type checking, so LGTM.