Update sbt-pgp to 2.3.1 (#285)

Co-authored-by: Jim Balhoff <jim@balhoff.org>

Author: scala-steward

project/plugins.sbt

@@ -1,4 +1,4 @@
 addSbtPlugin("com.github.sbt" % "sbt-native-packager" % "1.9.16")
 addSbtPlugin("com.eed3si9n" % "sbt-buildinfo" % "0.12.0")
 addSbtPlugin("com.github.sbt" % "sbt-git" % "2.1.0")
-addSbtPlugin("com.github.sbt" % "sbt-pgp" % "2.2.1")
+addSbtPlugin("com.github.sbt" % "sbt-pgp" % "2.3.1")