Marks Mac_ios post_backdrop_filter_perf_ios__timeline_summary to be unflaky (#101054)

Author: fluttergithubbot

.ci.yaml

@@ -3646,7 +3646,6 @@ targets:
     scheduler: luci
 
   - name: Mac_ios post_backdrop_filter_perf_ios__timeline_summary
-    bringup: true # Flaky https://github.com/flutter/flutter/issues/99855
     recipe: devicelab/devicelab_drone
     presubmit: false
     timeout: 60