Don't report CA2257 on nested types

src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/InteropServices/DynamicInterfaceCastableImplementation.cs

@@ -128,7 +128,7 @@ private static void AnalyzeType(SymbolAnalysisContext context, INamedTypeSymbol
 
             foreach (var member in targetType.GetMembers())
             {
-                if (!member.IsImplementationOfAnyExplicitInterfaceMember() && !member.IsStatic)
+                if (!member.IsImplementationOfAnyExplicitInterfaceMember() && !member.IsStatic && !member.IsType())
                 {
                     // We don't want to emit diagnostics when the member is an accessor method.
                     if (member is not IMethodSymbol { AssociatedSymbol: IPropertySymbol or IEventSymbol })

src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/InteropServices/DynamicInterfaceCastableImplementationTests.cs

@@ -1240,6 +1240,31 @@ static void I.M()
             await VerifyCSCodeFixAsync(source, fixedSource, CSharp.LanguageVersion.Preview, ReferenceAssemblies.Net.Net60);
         }
 
+        [Fact]
+        [WorkItem(7106, "htpts://github.com/dotnet/roslyn-analyzers/issues/7106")]
+        public async Task DynamicInterfaceCastableImplementation_NonStatic_NestedType()
+        {
+            string source = @"
+using System.Runtime.InteropServices;
+
+public interface IMyInterface
+{
+    void M();
+}
+
+[DynamicInterfaceCastableImplementation]
+internal interface IImpl : IMyInterface
+{
+    internal class C { }
+
+    void IMyInterface.M()
+    {
+    }
+}
+";
+            await VerifyCSAnalyzerAsync(source);
+        }
+
         private static Task VerifyCSAnalyzerAsync(string source)
         {
             return VerifyCSCodeFixAsync(source, source);