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.
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index c443523..b5c86f2 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -2540,7 +2540,8 @@
 
     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