Add tests for scala sttp client (jsonLibrary: circe) #946

Job	Run time
Build sbt/Scala client, servers (samples/client/petstore/java/okhttp-gson)	1m 1s
Build sbt/Scala client, servers (samples/client/petstore/scala-http4s)	52s
Build sbt/Scala client, servers (samples/client/petstore/scala-pekko)	57s
Build sbt/Scala client, servers (samples/server/petstore/scalatra)	1m 10s
Build sbt/Scala client, servers (samples/server/petstore/scala-lagom-server)	4m 5s
Build sbt/Scala client, servers (samples/client/petstore/scalaz)	1m 6s
Build sbt/Scala client, servers (samples/server/petstore/scala-http4s-server)	57s
Build sbt/Scala client, servers (samples/server/petstore/scala-pekko-http-server)	1m 2s
Build sbt/Scala client, servers (samples/server/petstore/scala-cask)	1m 26s
Build sbt/Scala client, servers (samples/server/petstore/scala-play-server)	4m 5s
Build sbt/Scala client, servers (samples/server/petstore/scala-akka-http-server)	1m 0s
	17m 41s

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