ci: update release with secret and target repo

[fadi-george]

Description

One Line Summary

• update create release pr to use target_repo & gh_push_token

Details

• needs target_repo to be passed in for prep-release otherwise the sdk-actions or whichever caller would set the github.repostiry to itself e.g. creating create release branch in sdk-actions instead of the flutter repo
• needs GH_PUSH_TOKEN otherwise the caller e.g. (sdk-acitons) would 403 / error when trying to create a release-branch or other changes
• updates checkout step to specify the repsitory and token
• updates create-pr to accept push token secret and the target-repo

Example of sdk-acitons w/o target_repo:
https://github.com/OneSignal/sdk-actions/actions/runs/19555353422/job/55996469655 (create release pr in sdk-acitons not the wrappers)

Example of sdk-actions w/o token:
https://github.com/OneSignal/sdk-actions/actions/runs/19556567680/job/56000216159 (403 error when trying to push to release branch)

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
  • If it is hard to explain how any codes changes are related to each other then it most likely needs to be more than one PR
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
  • Simplify with less code, followed by splitting up code into well named functions and variables, followed by adding comments to the code.
• I have reviewed this PR myself, ensuring it meets each checklist item
  • WIP (Work In Progress) is ok, but explain what is still in progress and what you would like feedback on. Start the PR title with "WIP" to indicate this.

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