Suppress incorrect CA2257 warnings

[Sergio0694]

This PR suppresses some incorrect CS2257 warnings that were polluting our build output. As per the docs:

"Since a type that implements IDynamicInterfaceCastable may not implement a dynamic interface in metadata, calls to an instance interface member that is not an explicit implementation defined on this type are likely to fail at run time. To avoid run-time errors, mark new interface members static."

This clearly doesn't apply to these cases, since these members were just nested types, and not something you can invoke.

[manodasanW]

Related to dotnet/roslyn-analyzers#7106