PYTHON-5669 setup-tests.sh should support --active

[aclark4life]

PYTHON-5669

Changes in this PR

Added USE_ACTIVE_VENV environment variable to setup-tests.sh. If non-zero, then uv run is run with uv run --active.

Test Plan

Tested local.

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?

[blink1073]

LGTM!