Update akka-http, akka-http-testkit to 10.2.8 (#273)

Co-authored-by: scala-steward <162267+scala-steward-for-moia[bot]@users.noreply.github.com>
Co-authored-by: Bendix Sältz <bendix@saeltz.de>

Author: 3 people

build.sbt

@@ -32,7 +32,7 @@ lazy val root = (project in file("."))
   .settings(mimaSettings)
 
 val akkaVersion     = "2.6.18"
-val akkaHttpVersion = "10.2.7"
+val akkaHttpVersion = "10.2.8"
 
 lazy val akkaDependencies = Seq(
   "com.typesafe.akka" %% "akka-stream"       % akkaVersion,