Add change indicator to `version-scheme` label

[fthomas]

See the second paragraph in https://github.com/scala-steward-org/scala-steward/pull/2925#issuecomment-1385868645.

Another alternative would be to leave the version-scheme label as is and add a new version-change label that indicates if the change is major, minor, or patch based on the used or inferred version scheme. For example, PRs labelled with version-change:patch should be safe to merge independent of the actual version scheme.