Fix string type check for property initialization

Updated the property type check to use EndsWith("##string") and EndsWith("##string?") instead of direct equality. This ensures correct initialization for string properties with type suffixes.

Author: ChrisPulman

src/ReactiveUI.SourceGenerators.Roslyn/ObservableAsProperty/ObservableAsPropertyGenerator{FromObservable}.Execute.cs

@@ -309,7 +309,7 @@ private static string GetPropertySyntax(ObservableMethodInfo propertyInfo)
         var isPartialProperty = string.Empty;
         var propertyType = propertyInfo.ObservableType;
         string? initVal;
-        if (propertyType.Equals("string") || propertyType.Equals("string?"))
+        if (propertyType.EndsWith("##string") || propertyType.EndsWith("##string?"))
         {
             initVal = $""" = "{propertyInfo.InitialValue}";""";
         }