PYTHON-5862 Cleanup lockless uv usage

[NoahStapp]

PYTHON-5862

Changes in this PR

Removes the no-op UV_NO_LOCK environment variable usage (it doesn't exist anywhere in uv's docs, pure hallucination) in our CI alongside several other confusing and non-functional changes introduced by #2902. Also fixes the persistent failure of test-auth-aws-ecs due to the lockfile removal.

Test Plan

Test infra changes.

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?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[NoahStapp]

Test failures will be resolved by PYTHON-5974.