add scalafmt (plugin) to scala-sttp4 client #29

Job	Run time
Build sbt/Scala (samples/client/petstore/scala-akka)	1m 13s
Build sbt/Scala (samples/client/petstore/scala-sttp4-jsoniter)	1m 7s
Build sbt/Scala (samples/client/petstore/scala-http4s)	1m 10s
Build sbt/Scala (samples/client/petstore/scalaz)	1m 17s
Build sbt/Scala (samples/client/petstore/scala-sttp-circe)	1m 6s
Build sbt/Scala (samples/client/petstore/scala-sttp)	1m 3s
Build sbt/Scala (samples/client/petstore/scala-pekko)	1m 7s
Build sbt/Scala (samples/client/petstore/scala-sttp4)	1m 3s
	9m 6s

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