Bumped maximal number of pipelines created by a single push

It could also be a single transaction initied from the server side. The limit itself is there for protection: before it landed, it was possible to import a project with 1000 tags and then run 1000 pipelines.

There's no strong rationale upstream for so low a limit, except that usually, people don't push more than a couple branches.

On the Mercurial side however, it's easy to rebase a bunch of stacked topics in one go, and it is very surprising to users if it doesn't lead to as many pipelines. In the absolute, I'd prefer at least some way to explain why all the pipelines weren't launch and provide an easy way to do so (hence avoiding that validation of N Merge request would go trough O(N^2) pipelines), but in the meanwhile bumping the value is good enough.

--HG-- branch : heptapod