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

tests: better determinism in test-chg.t chg tests fail pretty often with "Sample count: *" line disappearing. It disappears because the sample count is zero, in which case a custom message is printed. This commit makes the test succeed in that case. Differential Revision: https://phab.mercurial-scm.org/D11716