Update sbt-assembly to 2.3.1 (#211)

Author: scala-steward

project/plugins.sbt

@@ -1,4 +1,4 @@
-addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "2.3.0")
+addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "2.3.1")
 addSbtPlugin("de.heikoseeberger" % "sbt-header" % "5.10.0")
 addSbtPlugin("com.github.sbt" % "sbt-github-actions" % "0.24.0")
 addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.9.2")