Scala Steward could send WIP PRs for selected pre-releases

[larsrh]

Precise mechanism unclear, but I could envision something like this:

• cats wants to release a bleeding-edge, experimental version 3.0.0
• to test out how much breaks in the ecosystem, maintainers release 3.0.0-M1
• scala-steward sends non-mergeable WIP PRs to projects bumping to the pre-release in order to have CI builds run
• maintainers keep a close eye on all the PRs (maybe there could be a dashboard, although that's out of scope here: they can also be selected through GitHub search)

[exoego]

maintainers keep a close eye on all the PRs (maybe there could be a dashboard, although that's out of scope here: they can also be selected through GitHub search)

This sounds related to #961

[fthomas]

A first step towards this feature would be the ability to create regular PRs that bump versions to pre-releases. This is currently prevented by the implementation of Version.selectNext. So the first thing to do would be to have a variant of selectNext that does not exclude pre-release versions of a different version series.