typing: enable pytype processing on mercurial/upgrade_utils/actions.py

This was the suggested workaround for the pytype bug that caused this file to be
processed forever.

Differential Revision: https://phab.mercurial-scm.org/D10460

mercurial/upgrade_utils/actions.py

@@ -5,15 +5,13 b''
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
-# See https://github.com/google/pytype/issues/860
-# pytype: skip-file
-
 from __future__ import absolute_import
 
 from ..i18n import _
 from .. import (
     error,
     localrepo,
+    pycompat,
     requirements,
     revlog,
     util,
@@ -21,6 +19,13 b' from .. import ('
 
 from ..utils import compression
 
+if pycompat.TYPE_CHECKING:
+    from typing import (
+        List,
+        Type,
+    )
+
+
 # list of requirements that request a clone of all revlog if added/removed
 RECLONES_REQUIREMENTS = {
     requirements.GENERALDELTA_REQUIREMENT,
@@ -110,7 +115,7 b' class improvement(object):'
         return hash(self.name)
 
 
-allformatvariant = []
+allformatvariant = []  # type: List[Type['formatvariant']]
 
 
 def registerformatvariant(cls):