Update iOS SDK to 5.2.16

Author: github-actions[bot]

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

@@ -1,5 +1,5 @@
 <dependencies>
   <iosPods>
-    <iosPod name="OneSignalXCFramework" version="5.2.14" addToAllTargets="true" />
+    <iosPod name="OneSignalXCFramework" version="5.2.16" addToAllTargets="true" />
   </iosPods>
 </dependencies>