parser: force a `ValueError` to bytes before passing to `error.ParseError`

Authored by mharbison72.


parser: force a ValueError to bytes before passing to error.ParseError

I'm not sure what changed before pytype 09-09-2021 (from 04-15-2021), but this
started getting flagged. I think there's a pytype bug here, because I don't
see how .lower() can be getting called on a ValueError after it is forced to
a byte string. That's suppressed for now to make progress.

This fixes:

File "/mnt/c/Users/Matt/hg/mercurial/parser.py", line 219, in unescapestr: Function bytestr.__init__ was called with the wrong arguments [wrong-arg-types]
         Expected: (self, ints: Iterable[int])
  Actually passed: (self, ints: ValueError)
  Attributes of protocol Iterable[int] are not implemented on ValueError: __iter__
File "/mnt/c/Users/Matt/hg/mercurial/parser.py", line 219, in unescapestr: No attribute 'lower' on ValueError [attribute-error]
  In Union[ValueError, mercurial.pycompat.bytestr]

Differential Revision: https://phab.mercurial-scm.org/D11471