Fix test_sys_module_has_signatures: METH_NOARGS never has None text signature

METH_NOARGS functions always produce '($self, /)' as their __text_signature__
via signature_from_flags() in Objects/typeobject.c, not None.  Placing
sys.__dir__ in the no_signature set (which assertIsNone(__text_signature__))
therefore always fails.

Remove '__dir__' from no_signature.  Since __dir__ is non-public (starts with
'__') it is not included in the is_public() filter, so no assertion is made
about it in the supported-signatures loop either.  The '($self, /)' signature
returned by inspect.signature(sys.__dir__) (empty visible params) is correct.

sys.__getattr__ stays in no_signature: METH_VARARGS has no fallback in
signature_from_flags() so its __text_signature__ is genuinely None.

Author: johnslavik

Lib/test/test_inspect/test_inspect.py

@@ -6179,9 +6179,11 @@ def test_sys_module_has_signatures(self):
         no_signature = {'getsizeof', 'set_asyncgen_hooks'}
         no_signature |= {name for name in ['getobjects']
                          if hasattr(sys, name)}
-        # sys.__dir__ and sys.__getattr__ are plain METH_NOARGS/METH_VARARGS
-        # builtins without Argument Clinic text signatures.
-        no_signature |= {'__dir__', '__getattr__'}
+        # sys.__getattr__ is METH_VARARGS without an Argument Clinic signature.
+        # sys.__dir__ is METH_NOARGS; METH_NOARGS always produces '($self, /)'
+        # via signature_from_flags(), not None, so it must not be in no_signature.
+        # __dir__ is non-public so it is not checked in the supported loop either.
+        no_signature |= {'__getattr__'}
         self._test_module_has_signatures(sys, no_signature)
 
     def test_abc_module_has_signatures(self):