heptapod-ci: actually give pytest more time before timeout
`HGTEST_TIMEOUT` is overridden by `HGTEST_SLOWTIMEOUT` for tests marked as
slow, which `test-check-pytype.t` is. So this whole time the timeout was 1500s
(or 25 minutes), which is unfortunately not long enough for a *lot* of the
times it's run on the CI.
Differential Revision: https://phab.mercurial-scm.org/D11717
#require execbit
$ hg init repo
$ cd repo
$ echo foo > foo
$ chmod 644 foo
$ hg ci -qAm '644'
$ chmod 755 foo
$ hg ci -qAm '755'
reverting to rev 0
$ hg revert -a -r 0
reverting foo
$ hg st
M foo
$ hg diff --git
diff --git a/foo b/foo
old mode 100755
new mode 100644
$ cd ..