Update sbt-ci-release to 1.9.3 (#360)

Author: scala-steward

project/plugins.sbt

@@ -1,4 +1,4 @@
-addSbtPlugin("com.github.sbt"    % "sbt-ci-release" % "1.9.2")
+addSbtPlugin("com.github.sbt"    % "sbt-ci-release" % "1.9.3")
 addSbtPlugin("de.heikoseeberger" % "sbt-header"     % "5.10.0")
 addSbtPlugin("org.scoverage"     % "sbt-scoverage"  % "2.3.1")
 addSbtPlugin("org.scalameta"     % "sbt-scalafmt"   % "2.5.4")