Use the correct base branch in create-change.py

[OneBlue]

Summary of the Pull Request

This changes updates create-branch.py to target the correct branch

PR Checklist

• [ ] Closes: Link to issue #xxx
• [ ] Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• [ ] Tests: Added/updated if needed and all pass
• [ ] Localization: All end user facing strings can be localized
• [ ] Dev docs: Added/updated if needed
• [ ] Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed