Marks Mac_ios new_gallery_ios__transition_perf to be flaky (#96402)

diff --git a/.ci.yaml b/.ci.yaml
index 818b004..02b2476 100755
--- a/.ci.yaml
+++ b/.ci.yaml
@@ -3364,6 +3364,7 @@
     scheduler: luci
 
   - name: Mac_ios new_gallery_ios__transition_perf
+    bringup: true # Flaky https://github.com/flutter/flutter/issues/96401
     recipe: devicelab/devicelab_drone
     presubmit: false
     timeout: 60