Add tests for scala sttp client (jsonLibrary: circe) #943

Job	Run time
Build sbt/Scala client, servers (samples/client/petstore/java/okhttp-gson)	46s
Build sbt/Scala client, servers (samples/client/petstore/scalaz)	55s
Build sbt/Scala client, servers (samples/server/petstore/scalatra)	1m 1s
Build sbt/Scala client, servers (samples/server/petstore/scala-play-server)	3m 59s
Build sbt/Scala client, servers (samples/server/petstore/scala-lagom-server)	3m 59s
Build sbt/Scala client, servers (samples/server/petstore/scala-finch)	2m 26s
Build sbt/Scala client, servers (samples/server/petstore/scala-cask)	1m 25s
Build sbt/Scala client, servers (samples/server/petstore/scala-http4s-server)	50s
Build sbt/Scala client, servers (samples/client/petstore/scala-http4s)	1m 0s
Build sbt/Scala client, servers (samples/client/petstore/scala-pekko)	47s
Build sbt/Scala client, servers (samples/server/petstore/scala-pekko-http-server)	58s
Build sbt/Scala client, servers (samples/server/petstore/scala-akka-http-server)	1m 7s
	19m 13s

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