Make success message in buildkite_trigger_build print in green

Trivial change that makes the scheduled Buildkite build URL more visible—and in line with how the `create_pull_request` action similarly prints those success messages in green for a similar situation.

Author: AliSoftware

lib/fastlane/plugin/wpmreleasetoolkit/actions/common/buildkite_trigger_build_action.rb

@@ -28,7 +28,7 @@ def self.run(params)
         )
 
         if response.state == 'scheduled'
-          UI.message("Successfully scheduled new build. You can see it at '#{response.web_url}'")
+          UI.success("Successfully scheduled new build. You can see it at '#{response.web_url}'")
         else
           UI.crash!("Failed to start job\nError: [#{response}]")
         end