Broken Scala version upgrade when using sbt-github-actions

[NthPortal]

The first commit to update the Scala version only modifies ci.yml, but not build.sbt. The second commit to regenerate ci.yml then undoes the change.

See NthPortal/extra-predef#73 for example.

[fthomas]

Thanks for the report @NthPortal! typelevel/shapeless-3#25 and typelevel/ce3.g8#27 are other examples of this bug.

[fthomas]

A simple workaround for this issue would be to add a check in NurtureAlg.applyNewUpdate that the diff between the update branch and the base branch is non-empty.

I think that is easier than fixing the underlying issue that we're recording the Scala version that is used to compile the build as a dependency of the project. For that we would need to exclude Scala libraries from libraryDependencies after reload plugins.