Marks Mac platform_channel_sample_test_macos to be unflaky (#123702)

diff --git a/.ci.yaml b/.ci.yaml
index cd4736a..8cda8a4 100644
--- a/.ci.yaml
+++ b/.ci.yaml
@@ -2972,7 +2972,6 @@
       task_name: platform_view_macos__start_up
 
   - name: Mac platform_channel_sample_test_macos
-    bringup: true
     recipe: devicelab/devicelab_drone
     presubmit: false
     timeout: 60