Update sbt-mdoc to 2.3.8

Author: scala-steward

project/plugins.sbt

@@ -3,7 +3,7 @@ addSbtPlugin("com.github.sbt" % "sbt-unidoc" % "0.5.0")
 addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.5.10")
 // addSbtPlugin("com.github.sbt"   % "sbt-git"             % "2.0.0")
 addSbtPlugin("org.lyranthe.sbt" % "partial-unification" % "1.1.2")
-addSbtPlugin("org.scalameta" % "sbt-mdoc" % "2.3.5")
+addSbtPlugin("org.scalameta" % "sbt-mdoc" % "2.3.8")
 addSbtPlugin("org.scoverage" % "sbt-scoverage" % "2.0.0")
 // addSbtPlugin("com.eed3si9n" % "sbt-projectmatrix" % "0.8.0")