RepoLookupError: b"unknown revision 'e6cee6491fdf762cc0883352b3e28d8d7c93c6ef'"

It seems we catch the wrong exception in the loader code and that case is not covered by tests so we could not detect it.

Sentry Issue: SWH-LOADER-MERCURIAL-Z

RevlogError: RevlogError
  File "mercurial/revlog.py", line 816, in rev
    return self.index.rev(node)

LookupError: b'00changelog.i@e6cee6491fdf762cc0883352b3e28d8d7c93c6ef: no node'
  File "mercurial/localrepo.py", line 1847, in __getitem__
    rev = self.changelog.rev(changeid)
  File "mercurial/revlog.py", line 823, in rev
    raise error.LookupError(node, self.indexfile, _(b'no node'))

RepoLookupError: b"unknown revision 'e6cee6491fdf762cc0883352b3e28d8d7c93c6ef'"
  File "swh/loader/core/loader.py", line 414, in load
    self.store_data()
  File "swh/loader/mercurial/loader.py", line 412, in store_data
    for rev in revs:
  File "swh/loader/mercurial/loader.py", line 385, in get_hg_revs_to_load
    for rev in self._new_revs(self._latest_heads):
  File "swh/loader/mercurial/loader.py", line 363, in _new_revs
    rev = self._repo[hg_nodeid].rev()
  File "mercurial/localrepo.py", line 1882, in __getitem__
    _(b"unknown revision '%s'") % pycompat.bytestr(changeid)

Loading failure, updating to `failed` status