[CP-beta]Run {Platform} flutter_packaging builders on release candidates. (#168825)

This pull request is created by [automatic cherry pick workflow](https://github.com/flutter/flutter/blob/main/docs/releases/Flutter-Cherrypick-Process.md#automatically-creates-a-cherry-pick-request)
Please fill in the form below, and a flutter domain expert will evaluate this cherry pick request.

### Issue Link:
What is the link to the issue this cherry-pick is addressing?

https://github.com/flutter/flutter/issues/168745

### Changelog Description:
Explain this cherry pick in one line that is accessible to most Flutter developers. See [best practices](https://github.com/flutter/flutter/blob/main/docs/releases/Hotfix-Documentation-Best-Practices.md) for examples

N/A - Internal CI infra change.

### Impact Description:
What is the impact (ex. visual jank on Samsung phones, app crash, cannot ship an iOS app)? Does it impact development (ex. flutter doctor crashes when Android Studio is installed), or the shipping production app (the app crashes on launch)

Allows removing legacy logic in the `flutter_release_builder` recipe.

### Workaround:
Is there a workaround for this issue?

N/A

### Risk:
What is the risk level of this cherry-pick?

### Test Coverage:
Are you confident that your fix is well-tested by automated tests?

### Validation Steps:
What are the steps to validate that this fix works?

Merge on the candidate branch and observe post-submits.

.ci.yaml

@@ -6866,6 +6866,7 @@ targets:
     scheduler: release
     bringup: true # https://github.com/flutter/flutter/issues/126286
     enabled_branches:
+      - flutter-\d+\.\d+-candidate\.\d+
       - beta
       - stable
     properties:
@@ -6880,6 +6881,7 @@ targets:
     timeout: 60
     scheduler: release
     enabled_branches:
+      - flutter-\d+\.\d+-candidate\.\d+
       - beta
       - stable
     properties:
@@ -6896,6 +6898,7 @@ targets:
     timeout: 60
     scheduler: release
     enabled_branches:
+      - flutter-\d+\.\d+-candidate\.\d+
       - beta
       - stable
     properties:
@@ -6912,6 +6915,7 @@ targets:
     scheduler: release
     bringup: true
     enabled_branches:
+      - flutter-\d+\.\d+-candidate\.\d+
       - beta
       - stable
     properties: