Please choose:
You flagged it. Your tech lead made the call. Document it internally and move on — that is your limit of responsibility.
Ask your tech lead to add a note about the known bias in the product documentation. That creates a record without escalating.
Request a meeting with the product lead — one level above your tech lead — and present the validation data directly.
Send a formal written notice to the product lead and the ethics team, with the data attached. State clearly what you found and that you cannot sign off on silence before we ship.