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
$ cat >> $HGRCPATH << EOF
> [extensions]
> fastannotate=
> EOF
$ hg init repo
$ cd repo
changes to whitespaces
$ cat >> a << EOF
> 1
>
>
> 2
> EOF
$ hg commit -qAm '1'
$ cat > a << EOF
> 1
>
> 2
>
>
> 3
> EOF
$ hg commit -m 2
$ hg fastannotate -wB a
0: 1
0:
1: 2
0:
1:
1: 3