gpui_windows: Fix immovable windows skipping hit testing entirely (#59816)

Prior to this, marking a window as immovable would prevent the title bar
buttons working on windows.

Release Notes:

- N/A
9ac117693bLukas Wirth committed on 6/24/2026, 4:31:35 PM· committed by GitHubparent3b2acfe
1 file changedLine totals unavailable