Re-enable iOS transitions test in devicelab (#9097)

This reverts commit 326355f0f913c954f92aa74612daa78be22755dd.

dev/devicelab/manifest.yaml

diff --git a/dev/devicelab/manifest.yaml b/dev/devicelab/manifest.yaml
index 8e586c1..2a8960a 100644
--- a/dev/devicelab/manifest.yaml
+++ b/dev/devicelab/manifest.yaml
@@ -177,12 +177,12 @@
     stage: devicelab_ios
     required_agent_capabilities: ["has-ios-device"]
 
-  # flutter_gallery_ios__transition_perf:
-  #   description: >
-  #     Measures the performance of screen transitions in Flutter Gallery on
-  #     iOS.
-  #   stage: devicelab_ios
-  #   required_agent_capabilities: ["has-ios-device"]
+  flutter_gallery_ios__transition_perf:
+    description: >
+      Measures the performance of screen transitions in Flutter Gallery on
+      iOS.
+    stage: devicelab_ios
+    required_agent_capabilities: ["has-ios-device"]
 
   basic_material_app_ios__size:
     description: >