Save work on emitting ignored diagnostics pt 2 (#20696)

This should be another 2.5% on self check

Sequel to #20621

Author: hauntsaninja

mypy/checker.py

@@ -4754,7 +4754,7 @@ def check_simple_assignment(
                 self.msg.deleted_as_rvalue(rvalue_type, context)
             if isinstance(lvalue_type, DeletedType):
                 self.msg.deleted_as_lvalue(lvalue_type, context)
-            elif lvalue_type:
+            elif lvalue_type and not self.can_skip_diagnostics:
                 self.check_subtype(
                     # Preserve original aliases for error messages when possible.
                     rvalue_type,

mypy/checkexpr.py

@@ -2526,6 +2526,8 @@ def check_argument_types(
 
         The check_call docstring describes some of the arguments.
         """
+        if self.chk.can_skip_diagnostics:
+            return
         self.check_var_args_kwargs(arg_types, arg_kinds, context)
 
         check_arg = check_arg or self.check_arg