Pint ddtrace to safe version (3.12.0)

[bszabo]

Pinning ddtrace to version from before the deploy that had to be rolled back with yesterday's production incident. Version 3.12.0 has been confirmed as safe; version 3.12.1 causes excessive CPU loading and avalanche autoscaling.

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Make sure that the following steps are done before merging:

• Have a Site Reliability Engineer review the PR if you don't own all of the services impacted.
• If you are adding any new default values that need to be overridden when this change goes live, update internal repos and add an entry to the top of the CHANGELOG.
• Performed the appropriate testing.