Update sbt-scalafmt to 2.5.6

Author: typelevel-steward[bot]

project/plugins.sbt

@@ -2,7 +2,7 @@ addSbtPlugin("org.portable-scala" % "sbt-scala-native-crossproject" % "1.3.2")
 addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.18.2")
 addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.5.8")
 addSbtPlugin("org.scalameta" % "sbt-mdoc" % "2.6.2")
-addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.5")
+addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.6")
 addSbtPlugin("org.scoverage" % "sbt-scoverage" % "2.4.0")
 addSbtPlugin("org.typelevel" % "sbt-typelevel" % "0.8.0")
 addSbtPlugin("org.typelevel" % "sbt-typelevel-site" % "0.8.0")