typing: fix return type of logcmdutil.getrevs()

Fixes the following errors:

  Invalid type annotation "'Tuple[smartset.BaseSet, changesetdiffer]'"
  [invalid-annotation]
    No attribute 'BaseSet' on module 'mercurial.smartset'
  getrevs: bad option in return type [bad-return-type]
    Expected: Tuple[mercurial.smartset.abstractsmartset, changesetdiffer]
    Actually returned: Tuple[mercurial.smartset.baseset, None]

mercurial/logcmdutil.py

@@ -45,10 +45,11 b' from .utils import ('
 if pycompat.TYPE_CHECKING:
     from typing import (
         Any,
+        Optional,
         Tuple,
     )
 
-    for t in (Any, Tuple):
+    for t in (Any, Optional, Tuple):
         assert t
 
 
@@ -853,7 +854,7 b' def _initialrevs(repo, opts):'
 
 
 def getrevs(repo, pats, opts):
-    # type: (Any, Any, Any) -> Tuple[smartset.BaseSet, changesetdiffer]
+    # type: (Any, Any, Any) -> Tuple[smartset.abstractsmartset, Optional[changesetdiffer]]
     """Return (revs, differ) where revs is a smartset
 
     differ is a changesetdiffer with pre-configured file matcher.