hgweb: unbyteify the 100-continue check
The environment seems to be `str` or `tuple[int]`, and the same check in
`wsgicgi.py` is already `str` based, so I suspect this was wrong. I think what
happened here is that the string wasn't `r''` prefixed in 482d6f6dba91 like
`wsgicgi.py`, so it got wrongly byteified in 687b865b95ad when converting to
byte literals en masse.
test-convert-git.t
test-subrepo-git.t
test-patchbomb-tls.t