change label format to `version-scheme:$scheme after review

Author: mzuehlke

modules/core/src/main/scala/org/scalasteward/core/forge/data/NewPullRequestData.scala

@@ -287,7 +287,7 @@ object NewPullRequestData {
         SemVer.getChangeSpec(curr, next).map(c => s"semver-spec-${c.render}")
       }
       val versionSchemeLabel =
-        artifactIdToVersionScheme.get(u.mainArtifactId).map(vs => s"version-scheme-$vs")
+        artifactIdToVersionScheme.get(u.mainArtifactId).map(vs => s"version-scheme:$vs")
       List(earlySemVerLabel, semVerSpecLabel, versionSchemeLabel).flatten
     }
     val semverLabels =

modules/core/src/test/scala/org/scalasteward/core/nurture/NurtureAlgTest.scala

@@ -65,15 +65,15 @@ class NurtureAlgTest extends CatsEffectSuite with Http4sDsl[MockEff] {
              |```
              |</details>
              |
-             |labels: library-update, early-semver-minor, semver-spec-minor, version-scheme-early-semver, commit-count:1
+             |labels: library-update, early-semver-minor, semver-spec-minor, version-scheme:early-semver, commit-count:1
              |""".stripMargin.trim,
       head = "scala-steward:update/cats-effect-3.4.0",
       base = baseBranch,
       labels = List(
         "library-update",
         "early-semver-minor",
         "semver-spec-minor",
-        "version-scheme-early-semver",
+        "version-scheme:early-semver",
         "commit-count:1"
       )
     )