Upgrade dependencies: Scala 3.8.4, Scala.js 1.22.0, sbt-ci-release 1.12.0

[github-actions]

Upgraded

• Scala 3.8.3 -> 3.8.4 in build.sbt
• Scala.js (sbt plugin) 1.21.0 -> 1.22.0 in project/plugins.sbt (also updates scalaJSVersion transitively for scalajs-test-interface)
• sbt-ci-release 1.11.2 -> 1.12.0 in project/plugins.sbt
• sbt-git 2.0.1 added to project/plugins.sbt — required because sbt-ci-release 1.12.0 removed its sbt-git dependency, which this project uses for GitVersioning in publish.sbt

Skipped

• sbt 1.12.11 -> 2.0.6: major version — skipped for API/plugin compatibility
• scala-library:provided (plugin dep): not a real dependency to update

Verification

sbt ci-all passes across all 3 Scala versions (2.12.21, 2.13.18, 3.8.4) on both JVM and JS platforms.