Update sbt-reproducible-builds and set check resolver to staging

build.sbt

@@ -7,6 +7,7 @@
  * This file is part of the Apache Pekko project, which was derived from Akka.
  */
 
+import net.bzzt.reproduciblebuilds.ReproducibleBuildsPlugin.reproducibleBuildsCheckResolver
 import org.apache.pekko._
 
 ThisBuild / scalafixScalaBinaryVersion := scalaBinaryVersion.value
@@ -24,6 +25,9 @@ commands := commands.value.filterNot { command =>
   }
 }
 
+ThisBuild / reproducibleBuildsCheckResolver :=
+  "Apache Pekko Staging".at("https://repository.apache.org/content/groups/staging/")
+
 enablePlugins(
   UnidocRoot,
   UnidocWithPrValidation,