Fix @⁠HttpServiceClient example in reference manual

Closes gh-35363

Signed-off-by: NeatGuyCoding <15627489+NeatGuyCoding@users.noreply.github.com>

framework-docs/modules/ROOT/pages/integration/rest-clients.adoc

@@ -1201,12 +1201,12 @@ annotate HTTP interfaces as follows:
 [source,java,indent=0,subs="verbatim,quotes"]
 ----
 	@HttpServiceClient("echo")
-	public class EchoServiceA {
+	public interface EchoServiceA {
 		// ...
 	}
 
 	@HttpServiceClient("echo")
-	public class EchoServiceB {
+	public interface EchoServiceB {
 		// ...
 	}
 ----