Update sbt-scalafmt to 2.5.6

Author: scala-steward

project/plugins.sbt

@@ -4,7 +4,7 @@ addSbtPlugin("ch.epfl.scala" % "sbt-scalajs-bundler" % "0.21.1")
 addSbtPlugin("org.scalablytyped.converter" % "sbt-converter" % "1.0.0-beta39")
 
 addSbtPlugin("org.typelevel" % "sbt-tpolecat" % "0.5.2")
-addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.4")
+addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.6")
 
 // for reading npmDependencies from package.json
 libraryDependencies ++= Seq("com.lihaoyi" %% "upickle" % "2.0.0")