Update sbt-scalafmt to 2.5.6

Author: scala-steward

project/plugins.sbt

@@ -1,7 +1,7 @@
 addSbtPlugin("com.github.sbt" % "sbt-dynver" % "5.1.1")
 addSbtPlugin("com.github.sbt" % "sbt-pgp" % "2.3.1")
 addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "1.1.4")
-addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.5")
+addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.6")
 addSbtPlugin("com.eed3si9n" % "sbt-buildinfo" % "0.13.1")
 addSbtPlugin("com.github.sbt" % "sbt-header" % "5.11.0")
 addSbtPlugin("org.scala-sbt" % "sbt-contraband" % "0.8.0")