iOS: Use UIPasteboard string property in SystemClipboard::getTextFromClipboard() to ensure that only NSStrings are retrieved

modules/juce_gui_basics/native/juce_ios_Windowing.mm

@@ -658,7 +658,7 @@ void SystemClipboard::copyTextToClipboard (const String& text)
 
 String SystemClipboard::getTextFromClipboard()
 {
-    return nsStringToJuce ([[UIPasteboard generalPasteboard] valueForPasteboardType: @"public.text"]);
+    return nsStringToJuce ([[UIPasteboard generalPasteboard] string]);
 }
 
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