Update sbt-mdoc to 2.8.0 (flink-extended#301)

Co-authored-by: alexey <117519424+novakov-alexey@users.noreply.github.com>

Author: scala-steward

project/plugins.sbt

@@ -1,8 +1,5 @@
-// addSbtPlugin("org.xerial.sbt" % "sbt-sonatype"   % "3.12.2")
-// addSbtPlugin("com.github.sbt" % "sbt-pgp"        % "2.3.1")
 addSbtPlugin("org.scalameta"  % "sbt-scalafmt" % "2.5.5")
-addSbtPlugin("org.scalameta"  % "sbt-mdoc"     % "2.7.2")
+addSbtPlugin("org.scalameta"  % "sbt-mdoc"     % "2.8.0")
 addSbtPlugin("com.github.sbt" % "sbt-release"  % "1.4.0")
-// addSbtPlugin("com.github.sbt" % "sbt-git"        % "2.1.0")
 addSbtPlugin("com.github.sbt" % "sbt-protobuf"         % "0.8.3")
 addSbtPlugin("io.shiftleft"   % "sbt-ci-release-early" % "2.1.11")