Marks Linux_android platform_channels_benchmarks to be flaky (#135106)

<!-- meta-tags: To be used by the automation script only, DO NOT MODIFY.
{
  "name": "Linux_android platform_channels_benchmarks"
}
-->
Issue link: https://github.com/flutter/flutter/issues/135105

.ci.yaml

@@ -2520,6 +2520,7 @@ targets:
       task_name: slider_perf_android
 
   - name: Linux_android platform_channels_benchmarks
+    bringup: true # Flaky https://github.com/flutter/flutter/issues/135105
     recipe: devicelab/devicelab_drone
     presubmit: false
     timeout: 60