Potential fix for code scanning alert no. 34: Cast to same type

[DoubledDoge]

Potential fix for https://github.com/DoubledDoge/typeguard/security/code-scanning/34

In general, to fix “cast to same type” issues, remove explicit casts where the compiler already knows the expression has the same type, relying on implicit typing and conversions instead. This keeps code clearer and avoids implying there is some special conversion or nullability change when there is not.

Here, on line 45 in src/TypeGuard.Winforms/WinFormsInput.cs, the expression (string?)_control.Invoke(() => _control.Text) is assigned to string? text. Since CodeQL has determined the static type of _control.Invoke(() => _control.Text) is string, the (string?) cast is unnecessary: a non-nullable string can be implicitly converted to string?. The best fix that preserves functionality is to remove only the cast and leave the rest of the expression as is. No new imports or helper methods are required. The edit is restricted to that single line inside the GetInput method.

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