Update sbt-coveralls to 1.3.15

Author: scala-steward

project/plugins.sbt

@@ -3,7 +3,7 @@ addSbtPlugin("com.typesafe.sbt" % "sbt-git" % "1.0.2")
 addSbtPlugin("com.github.sbt" % "sbt-site" % "1.6.0")
 addSbtPlugin("com.typesafe.sbt" % "sbt-ghpages" % "0.6.3")
 addSbtPlugin("org.scoverage" % "sbt-scoverage" % "2.0.0")
-addSbtPlugin("org.scoverage" % "sbt-coveralls" % "1.3.14")
+addSbtPlugin("org.scoverage" % "sbt-coveralls" % "1.3.15")
 addSbtPlugin("com.github.sbt" % "sbt-github-actions" % "0.24.0")
 addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.2")
 addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.5.10")