Update mdoc, sbt-mdoc to 2.3.8

Author: scala-steward

project/plugins.sbt

@@ -6,7 +6,7 @@ addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.5.12")
 addSbtPlugin("com.github.sbt" % "sbt-git" % "2.1.0")
 addSbtPlugin("com.github.sbt" % "sbt-native-packager" % "1.11.1")
 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" % "2.3.1")
 addSbtPlugin("com.simplytyped" % "sbt-antlr4" % "0.8.3")
 addSbtPlugin("com.github.sbt" % "sbt-site-asciidoctor" % "1.5.0")