NpgsqlArrayConverter makes certain assumptions that its input and output types are reference types. We don't (currently) actually support mapping array types which aren't array or List, but the exceptions thrown from NpgsqlArrayConverter actually make it impossible to ignore an ImmutableArray property that requires value conversion (see dotnet/efcore#35329 when this was raised).

Do at least the minimum work to make sure that NpgsqlArrayConverter can be constructed without exceptions.