tests: register test-merge-combination.t as small but slow
run-tests.py use file size as an heuristic for test run time. The new
`test-merge-combination.t` is a small file that do a lot of processing. As a
result it tend to be scheduled really late but delay the full test run by a lot.
On an example test run, the one-before-last test completed 279s after the start
of the run, while `test-merge-combination.t` finished 355s after it. A 76s
delay. This delay can be avoided since `test-merge-combination.t` only got started
175s after the start of the run.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).