Bump OneSignal iOS SDK to 5.2.1

Fixes OneSignal iOS SDK mac catalyst build error

Author: shepherd-l

com.onesignal.unity.ios/Editor/OneSignaliOSDependencies.xml

@@ -1,5 +1,5 @@
 <dependencies>
     <iosPods>
-            <iosPod name="OneSignalXCFramework" version="5.2.0" addToAllTargets="true" />
+            <iosPod name="OneSignalXCFramework" version="5.2.1" addToAllTargets="true" />
     </iosPods>
 </dependencies>