gh-122864: Fix a test_funcattrs.test___builtins__ when executing directly (#124845)

Previously when executing ``test_functattrs.test___builtins__`` directly, it failed because the fact, that ``__builtins__`` is refers to the built-in module ``builtins`` while it's expects a ``__builtins__.__dict__``. But when this test is being run from another module, then ``__builtins__`` is refers to ``builtins.__dict__``. Now this part of the behaviour is covered.
---------

Co-authored-by: Victor Stinner <[email protected]>

Author: mbyrnepr2

Lib/test/test_funcattrs.py

@@ -98,7 +98,12 @@ def test___globals__(self):
                              (AttributeError, TypeError))
 
     def test___builtins__(self):
-        self.assertIs(self.b.__builtins__, __builtins__)
+        if __name__ == "__main__":
+            builtins_dict = __builtins__.__dict__
+        else:
+            builtins_dict = __builtins__
+
+        self.assertIs(self.b.__builtins__, builtins_dict)
         self.cannot_set_attr(self.b, '__builtins__', 2,
                              (AttributeError, TypeError))
 
@@ -108,7 +113,7 @@ def func(s): return len(s)
         ns = {}
         func2 = type(func)(func.__code__, ns)
         self.assertIs(func2.__globals__, ns)
-        self.assertIs(func2.__builtins__, __builtins__)
+        self.assertIs(func2.__builtins__, builtins_dict)
 
         # Make sure that the function actually works.
         self.assertEqual(func2("abc"), 3)