Update sbt-pgp to 2.3.1 (#184)

Author: scala-steward

project/plugins.sbt

@@ -1,5 +1,5 @@
 addSbtPlugin("org.xerial.sbt" % "sbt-sonatype" % "3.12.2")
-addSbtPlugin("com.github.sbt" % "sbt-pgp"      % "2.3.0")
+addSbtPlugin("com.github.sbt" % "sbt-pgp"      % "2.3.1")
 addSbtPlugin("org.scalameta"  % "sbt-scalafmt" % "2.5.2")
 addSbtPlugin("org.scalameta"  % "sbt-mdoc"     % "2.6.1")
 addSbtPlugin("com.github.sbt" % "sbt-release"  % "1.4.0")