Testing on unreleased Julia versions was disabled in #688 since it basically always failed - usually in the allocation tests, which also cause test errors in this PR.

That was nightly, that's not very related to testing on prereleases which is much safer. Nightly can fail because Julia base itself is broken which makes it not necessarily a good signal for anything useful. Prereleases shouldn't be broken as they should already be pretty close to being a release. The allocation tests failing here means that they will be likely breaking when the release is made unless someone opens an issue, which is a pretty good thing to know. In fact, if someone doesn't open that MWE on Julia itself in like 1 month it will just be a regression 😅

In addition, pre just runs the regular release CI when you are not in a pre-release period and thus consuming a lot of wasteful CI cycles.