test: generate the `test-sparse-revlog` artifact when slow-test is allowed
The `test-sparse-revlog.t` logic requires a large bundle to be generated. This
bundle can be reused from one run to the next but its initial generation is
slow. With this patch, if the bundle is missing and slow tests are permitted,
the bundle will be generated during the test run.
This should ensure that CI run this test.
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).