LTS nightly TASTy check

[Gedochao]

• just an adjustment to work with Add a Scala 3.9 nightly CI job scala3#27043

[WojciechMazur]

Gave the approval, but I don't remember what was the conclusion about the state of nightly release.

On main (Next) every nightly is always assumed experimental, becuse, well it's nightly
I think we had a discussion about it in the past, but I don't remember conclusion if we should do the same in LTS line for nightlies, I think we should. But then we cannot just bump TASTy minor since that minor is already in use by 3.10...

Still following these rules would be the safest, and would discurage users from publishing with nightly:

   *      - in release branch is always equal to $minor
   *      - in main (NIGHTLY) is always experimental

[tgodzik]

Could we just set the version to experimental on the 3.9 branch and change it to stable on releases?

[Gedochao]

As discussed on Scala Core, we won't make 3.9 LTS nightlies have experimental TASTY.
Closing this.