Adjust BWC candidates in retention lease BWC tests (#40562)
Adjust BWC candidates in retention lease BWC tests (#40562)

We test BWC with nodes older than 6.7.0 since such nodes would not
understand retention lease sync requests. However, we do not need to
test compatbility with nodes on or after 6.7.0 since we know these nodes
understand retention lease sync requests, which are already exercised in
other tests. Therefore, we can skip these versions when running the BWC
tests and only test against versions that do not understand retention
lease sync requests.
vroyer/elassandra,strapdata/elassandra,vroyer/elassandra,vroyer/elassandra,strapdata/elassandra,strapdata/elassandra,strapdata/elassandra,strapdata/elassandra