Update sbt-mdoc to 2.2.3 (#357)

Author: scala-steward

project/plugins.sbt

@@ -4,7 +4,7 @@ addSbtPlugin("org.scala-js"         % "sbt-scalajs"              % "1.1.0")
 addSbtPlugin("org.scalameta"        % "sbt-scalafmt"             % "2.4.0")
 addSbtPlugin("com.47deg"            % "sbt-microsites"           % "1.2.1")
 addSbtPlugin("org.scoverage"        % "sbt-scoverage"            % "1.6.1")
-addSbtPlugin("org.scalameta"        % "sbt-mdoc"                 % "2.2.2")
+addSbtPlugin("org.scalameta"        % "sbt-mdoc"                 % "2.2.3")
 addSbtPlugin("de.heikoseeberger"    % "sbt-header"               % "5.6.0")
 addSbtPlugin("com.alejandrohdezma" %% "sbt-codecov"              % "0.2.0")
 addSbtPlugin("com.alejandrohdezma" %% "sbt-github"               % "0.8.2")