Update mdoc, sbt-mdoc to 2.6.0 (#392)

Author: scala-steward

project/plugins.sbt

@@ -7,7 +7,7 @@ addSbtPlugin("org.typelevel" % "sbt-typelevel" % "0.7.3")
 addSbtPlugin("org.typelevel" % "sbt-typelevel-site" % "0.7.3")
 addSbtPlugin("org.typelevel" % "sbt-typelevel-github-actions" % "0.7.3")
 addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.16.0")
-addSbtPlugin("org.scalameta" % "sbt-mdoc" % "2.5.4")
+addSbtPlugin("org.scalameta" % "sbt-mdoc" % "2.6.0")
 addSbtPlugin("org.portable-scala" % "sbt-scala-native-crossproject" % "1.3.2")
 addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.4.17")
 addSbtPlugin("com.eed3si9n" % "sbt-buildinfo" % "0.12.0")