[tests/link sdk] Preserve a required method in System.Private.CoreLib…

… to work around a bug in .NET 6.

Ref: dotnet/runtime#46908.

tests/linker/ios/link sdk/dotnet/extra-linker-defs.xml

@@ -11,4 +11,11 @@
 	<assembly fullname="Xamarin.iOS">
 		<type fullname="CoreBluetooth.CBUUID" preserve="field" />
 	</assembly>
+	<assembly fullname="System.Private.CoreLib">
+		<type fullname="System.Runtime.Loader.AssemblyLoadContext">
+			<!-- https://github.com/dotnet/runtime/issues/46908 -->
+			<!-- native-library.c: netcore_resolve_with_resolving_event () -->
+			<method name="MonoResolveUnmanagedDllUsingEvent" />
+		</type>
+	</assembly>
 </linker>