PYTHON-5467

Changes in this PR

Use the CODECOV_TOKEN secret to upload codecov to avoid the error: Upload failed: {"message":"Token required because branch is protected"}

Test Plan

We'll need to merge to be able to make sure it works.

Checklist

Checklist for Author

• Did you update the changelog (if necessary)?
• Is there test coverage?
• Is any followup work tracked in a JIRA ticket? If so, add link(s).

Checklist for Reviewer

• Does the title of the PR reference a JIRA Ticket?
• Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
• Is all relevant documentation (README or docstring) updated?