Per the discussion in #drivers, retryable writes are specified to not be performed when in transaction context. retryable_writes_spec.rb has no mention of the word "transaction", and retryable_spec.rb has the following:

allow(session).to receive(:in_transaction?).and_return(false)

These tests need to be expanded to test that writes are not retried when transactions are used.

Neither modern nor legacy retryable writes should be performed when in a transaction.