Avoid error for creating underscore object

Don't show an error about calling a function named '_' directly when '_'
refers to a class named '_' and we're actually creating an object.
Having a class named '_' is probably rare and using it directly is
probably even rarer, but the other parts of the PR only deal with
functions, not classes, so we probably should keep that consistent.

Author: pranavrajpal

mypy/checkexpr.py

@@ -334,7 +334,9 @@ def visit_call_expr_inner(self, e: CallExpr, allow_none_return: bool = False) ->
                 and callee_type.implicit):
             self.msg.untyped_function_call(callee_type, e)
 
-        if isinstance(callee_type, CallableType) and callee_type.name == "_":
+        if (isinstance(callee_type, CallableType)
+                and not callee_type.is_type_obj()
+                and callee_type.name == "_"):
             self.msg.underscore_function_call(e)
             return AnyType(TypeOfAny.from_error)