Update sbt-ci-release to 1.5.6

Author: scala-steward

project/plugins.sbt

@@ -17,6 +17,6 @@ addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.4.2")
 
 addSbtPlugin("io.github.davidgregory084" % "sbt-tpolecat" % "0.1.16")
 
-addSbtPlugin("com.geirsson" % "sbt-ci-release" % "1.5.5")
+addSbtPlugin("com.geirsson" % "sbt-ci-release" % "1.5.6")
 
 addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "0.5.3")