Update mdoc, sbt-mdoc to 2.5.1

Author: scala-steward

project/plugins.sbt

@@ -2,5 +2,5 @@ addSbtPlugin("org.typelevel"  % "sbt-tpolecat"         % "0.5.0")
 addSbtPlugin("org.scalameta"  % "sbt-scalafmt"         % "2.5.2")
 addSbtPlugin("com.github.sbt" % "sbt-ci-release"       % "1.5.10")
 addSbtPlugin("com.47deg"      % "sbt-microsites"       % "1.3.4")
-addSbtPlugin("org.scalameta"  % "sbt-mdoc"             % "2.5.0")
+addSbtPlugin("org.scalameta"  % "sbt-mdoc"             % "2.5.1")
 addSbtPlugin("com.codecommit" % "sbt-spiewak-sonatype" % "0.23.0")