C#: Ignore late bound methods in MustBeVariantAnalyzer

If symbol is late bound (as is the case when using `dynamic`) we can't obtain the symbol to analyze the usage of `[MustBeVariant]`.

modules/mono/editor/Godot.NET.Sdk/Godot.SourceGenerators.Tests/TestData/Sources/MustBeVariant.GD0301.cs

@@ -66,6 +66,12 @@ public class MustBeVariantGD0301
         Method<Rid[]>();
     }
 
+    public void MethodCallDynamic()
+    {
+        dynamic self = this;
+        self.Method<object>();
+    }
+
     public void Method<[MustBeVariant] T>()
     {
     }