tests: fix http-bad-server expected errors for python 3.10 (issue6643)
The format of the error message changed with this version of Python.
This also removes obsolete Python 3 checks.
Issue351: mq: qrefresh can create extra revlog entry
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ hg qinit
$ echo b > b
$ hg ci -A -m foo
adding b
$ echo cc > b
$ hg qnew -f foo.diff
$ echo b > b
$ hg qrefresh
$ hg debugindex b
rev linkrev nodeid p1-nodeid p2-nodeid
0 0 1e88685f5dde 000000000000 000000000000