[Expo][iOS] Fix Swift AppDelegate plugin for @main annotation (Expo SDK 55+)

Expo SDK 55 adopted Swift 6, changing AppDelegate.swift from
@UIApplicationMain to @main. The config plugin used /@UIApplicationMain/
as a regex anchor to inject `import TSBackgroundFetch`, which silently
fails on SDK 55+.

Update the regex to /@(UIApplication)?main/ so it matches both
@UIApplicationMain (SDK 53-54) and @main (SDK 55+).

Author: mickeypause

expo/plugin/src/iOSPlugin.ts

@@ -66,7 +66,7 @@ const modifySwiftAppDelegate = (src:string) => {
     tag: "react-native-background-fetch-import",
     src,
     newSrc: "import TSBackgroundFetch",
-    anchor: /@UIApplicationMain/,
+    anchor: /@(UIApplication)?main/,
     offset: -1,
     comment: "//",
   }).contents;