Merge pull request #490 from scala-steward/update/sbt-ci-release-1.5.6

Update sbt-ci-release to 1.5.6

Author: mergify[bot]

project/plugins.sbt

@@ -1,7 +1,7 @@
 addSbtPlugin("io.github.davidgregory084" % "sbt-tpolecat" % "0.1.16")
 addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.9.26")
 addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.4.2")
-addSbtPlugin("com.geirsson" % "sbt-ci-release" % "1.5.5")
+addSbtPlugin("com.geirsson" % "sbt-ci-release" % "1.5.6")
 addSbtPlugin("com.47deg" % "sbt-microsites" % "1.3.2")
 addSbtPlugin("com.eed3si9n" % "sbt-unidoc" % "0.4.3")
 addSbtPlugin("com.thoughtworks.sbt-api-mappings" % "sbt-api-mappings" % "3.0.0")