localrepo: fix conversion of exceptions to strings flagged by pytype This is the same as e571fec5b606. I assume the 3 similar uses of `bytestr` in `__getitem__()` are OK (even though pytype also flags them), because there is apparently test coverage for 2 of the 3 cases. Differential Revision: https://phab.mercurial-scm.org/D10131

[workspace]
members = ["hg-core", "hg-cpython", "rhg"]
exclude = ["chg", "hgcli"]