Fixes Appearance user interface style when app run from background (#…

…46021)

Summary:
Fixes #46015.

## Changelog:

[IOS] [FIXED] - Fixes Appearance user interface style when app run from background

Pull Request resolved: #46021

Test Plan: Demo in #46015.

Reviewed By: christophpurrer

Differential Revision: D61536857

Pulled By: cipolleschi

fbshipit-source-id: ee06cb25b5fc4fa72d646efe212738e54b9ef858

packages/react-native/React/CoreModules/RCTAppearance.mm

@@ -70,8 +70,13 @@ void RCTUseKeyWindowForSystemStyle(BOOL useMainScreen)
     return appearances[@(traitCollection.userInterfaceStyle)];
   }
 
+  if (!traitCollection) {
+    traitCollection = [UITraitCollection currentTraitCollection];
+  }
+
   UIUserInterfaceStyle systemStyle = sUseKeyWindowForSystemStyle ? RCTKeyWindow().traitCollection.userInterfaceStyle
                                                                  : traitCollection.userInterfaceStyle;
+
   return appearances[@(systemStyle)] ?: RCTAppearanceColorSchemeLight;
 }