Bring native_assets ios tests out of staging (#135015)

Move test added in https://github.com/flutter/flutter/pull/130494 out of staging.

* https://ci.chromium.org/ui/p/flutter/builders/luci.flutter.staging/Mac_ios%20native_assets_ios
* https://ci.chromium.org/ui/p/flutter/builders/luci.flutter.staging/Mac_ios%20native_assets_ios_simulator

> Monitor the CI results of the new shard on the [Flutter build dashboard](https://flutter-dashboard.appspot.com/#/build). After 50 consecutive passing builds without any flakes, the flake bot will create a PR to remove the bringup: true parameter from .ci.yaml in the Framework tree. This will allow the test to block the tree, preventing breakages. With this change, the new shard will start running in presubmit automatically, unless specify presubmit: false.

https://github.com/flutter/flutter/wiki/Adding-a-new-Test-Shard#steps-to-add-a-new-framework-test-shard

Umbrella issue:

* https://github.com/flutter/flutter/issues/129757

.ci.yaml

@@ -4103,7 +4103,6 @@ targets:
   - name: Mac_ios native_assets_ios_simulator
     recipe: devicelab/devicelab_drone
     presubmit: false
-    bringup: true # TODO(dacoharkes): Set to false in follow up PR and check that test works on CI.
     timeout: 60
     properties:
       tags: >
@@ -4113,7 +4112,6 @@ targets:
   - name: Mac_ios native_assets_ios
     recipe: devicelab/devicelab_drone
     presubmit: false
-    bringup: true # TODO(dacoharkes): Set to false in follow up PR and check that test works on CI.
     timeout: 60
     properties:
       tags: >