typing: adjust `mercurial.util.iterlines()` to accept any `Iterable`

In a local pytype run on the extensions, this fixes:

    File "/mnt/c/Users/Matt/hg/hgext/phabricator.py", line 788, in maketext:
        Function mercurial.util.iterlines was called with the wrong arguments [wrong-arg-types]
             Expected: (iterator: Iterator[bytes])
      Actually passed: (iterator: list)
      Attributes of protocol Iterator[bytes] are not implemented on list: __next__

mercurial/util.py

@@ -60,6 +60,7 b' from .utils import ('
 
 if pycompat.TYPE_CHECKING:
     from typing import (
+        Iterable,
         Iterator,
         List,
         Optional,
@@ -2910,7 +2911,7 b' def iterfile(fp):'
 
 
 def iterlines(iterator):
-    # type: (Iterator[bytes]) -> Iterator[bytes]
+    # type: (Iterable[bytes]) -> Iterator[bytes]
     for chunk in iterator:
         for line in chunk.splitlines():
             yield line