[Mono.Android] Suppress IL2068 on ManagedTypeManager.GetTypeForSimpleReference

The Java.Interop bump (external/Java.Interop -> 6820a9cb) shifted the
trim-analysis warning on `ManagedTypeManager.GetTypeForSimpleReference`:
its return value flows from the un-annotated `out` parameter of
`ManagedTypeMapping.TryGetType (string, out Type)`, so it no longer
satisfies the method's `[return: DynamicallyAccessedMembers]` and the
trimmer now reports IL2068 (previously IL2063).

This unsuppressed warning inflates the trim warning count and breaks the
`BuildHasTrimmerWarnings` expectations. Mirror the existing IL2063
suppression on the sibling `TrimmableTypeMapTypeManager.GetTypeForSimpleReference`.
`ManagedTypeManager` is removed in #11643.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: simonrozsival

src/Mono.Android/Microsoft.Android.Runtime/ManagedTypeManager.cs

@@ -143,6 +143,7 @@ protected override IEnumerable<Type> GetTypesForSimpleReference (string jniSimpl
 		}
 	}
 
+	[UnconditionalSuppressMessage ("Trimming", "IL2068", Justification = "Temporary suppression until ManagedTypeMapping type entries carry DAM annotations.")]
 	[return: DynamicallyAccessedMembers (MethodsConstructors)]
 	protected override Type? GetTypeForSimpleReference (string jniSimpleReference)
 	{