ci: Fix `create-update-issues` workflow secret access

[Gudahtt]

Explanation

The create-update-issues workflow was failing because it didn't have access to the secrets it needed. The CORE_CREATE_UPDATE_ISSUES_TOKEN secret is only available on hte default-branch environment.

The workflow has been updated to use that environment so that it may access the secret.

Example failure: https://github.com/MetaMask/core/actions/runs/11633589453/job/32399521142

References

Fixes bug introduced in https://github.com/MetaMask/core/pull/4763

Changelog

N/A

Checklist

• [x] I've updated the test suite for new or updated code as appropriate
• [x] I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• [x] I've highlighted breaking changes using the "BREAKING" category above as appropriate
• [x] I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes