chore: update release action to not create the release branch but just open PR

[sethkfman]

Description

This PR makes a minor change to make the release action depend on an existing release branch before running the action. The new action will create a PR for the release branch and creating a PR for the changelog and version bump against the release branch.

Related issues

Fixes:

Manual testing steps

1. Confirm there is a release branch
2. Run the GH action
3. See successful run and 2 PRs

Screenshots/Recordings

Before

NA

After

• Example PR: feat: 9.9.9 #11887
• Example Changelog PR: chore: chore/9.9.9-Changelog #11888
• Successful Action Run: https://github.com/MetaMask/metamask-mobile/actions/runs/11411806607

Pre-merge author checklist

• I’ve followed MetaMask Contributor Docs and MetaMask Mobile Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[NicolasMassart]

Looks good to me.