Update sbt-scalafmt to 2.5.6 (#1277)

Co-authored-by: scala-steward-asf[bot] <147768647+scala-steward-asf[bot]@users.noreply.github.com>

Author: scala-steward-asf[bot]

project/plugins.sbt

@@ -16,7 +16,7 @@ addSbtPlugin("com.github.sbt" % "sbt-license-report" % "1.9.0")
 addSbtPlugin("com.lightbend.sbt" % "sbt-bill-of-materials" % "1.0.2")
 // discipline
 addSbtPlugin("com.github.sbt" % "sbt-header" % "5.11.0")
-addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.5")
+addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.6")
 addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "1.1.4")
 addSbtPlugin("com.github.sbt" % "sbt-java-formatter" % "0.9.0")