Fix snapshot versions calculation when the current version ends with -RC.

[Gedochao]

Release candidate versions seem to be breaking the snapshot version calculation, which in turn, among other things, breaks the scala-cli-src script.

▶ scala-cli-src version
# (...)
# 1 targets failed
# show 1 targets failed
# finalPublishVersion java.lang.NumberFormatException: For input string: "0-RC1"
#     java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
#    java.base/java.lang.Integer.parseInt(Integer.java:668)
#     java.base/java.lang.Integer.parseInt(Integer.java:786)
#     scala.collection.StringOps$.toInt$extension(StringOps.scala:908)
#     ammonite.$file.project.publish.$anonfun$computePublishVersion$4(publish.sc:73)
#     scala.Option.flatMap(Option.scala:283)
#     ammonite.$file.project.publish.computePublishVersion(publish.sc:69)
#     ammonite.$file.project.publish.$anonfun$finalPublishVersion$5(publish.sc:113)
#     mill.define.Task$TraverseCtx.evaluate(Task.scala:380)

After the fix, seems to work fine.

▶ scala-cli-src version
# (...)
# Scala CLI version: 1.0.1-SNAPSHOT
# Scala version (default): 3.2.2