Issue #26782: Acknowledge the incomplete status of __all__ in 3.5

Handle is probably meant to be excluded, and STARTUPINFO will be added to
__all__ in 3.6.

Lib/test/test_subprocess.py

@@ -2540,7 +2540,8 @@ class MiscTests(unittest.TestCase):
 
     def test__all__(self):
         """Ensure that __all__ is populated properly."""
-        intentionally_excluded = set(("list2cmdline",))
+        # STARTUPINFO added to __all__ in 3.6
+        intentionally_excluded = {"list2cmdline", "STARTUPINFO", "Handle"}
         exported = set(subprocess.__all__)
         possible_exports = set()
         import types