Ok, so looking at what @3arthqu4ke did previously we are caught in a bit of a vicious cycle if a new mc version cannot be launched by headlessmc, because we in turn need the mc-runtime-test-mod to test if headlessmc launches in headlessmc's CI.

HeadlessMc workflows should be able to build the mc-runtime-test-mod from a branch of mc-runtime-test(-mod), if there is no mc-runtime-test release with that jar available yet.

Then the workflow could look as follows:

• Create a branch here for a new version of Mc.
• Refine HeadlessMc until it can launch all modloaders on that version with the mod from that branch.
• Release new HeadlessMc version that supports the new version of Mc.
• Update HeadlessMc version in that branch
• Merge and release new mc-runtime-test
• Update HeadlessMc CI to use new mc-runtime-test release