[actions] fix weekly action to "work"

[jonathanpeppers]

This pull request updates the .github/workflows/weekly-stable-updates.yml file to enhance the workflow for creating weekly stable updates issues. The changes improve issue management by preventing duplicate issues, adding permissions, and assigning issues to the appropriate assignee.

Workflow Enhancements:

• Added permissions block to allow writing to issues.
• Updated the schedule trigger formatting for clarity.

Issue Management Improvements:

• Introduced a check to prevent duplicate issues by searching for existing issues with the same title before creating a new one.
• Added a step to assign the newly created issue to the @copilot user using the gh CLI.

Miscellaneous Updates:

• Added id: create-issue to the "Create weekly stable updates issue" job for referencing outputs in subsequent steps.