Fix redis cache for python3
Fix redis cache for python3

According to the redis-py docs, zrank will return the 0 based index for
the value in the sorted set.  So the logic here wasn't right to begin
with (It just means that a value at the 0-th position would never show
up as cached).  Need to compare against None to know if the value
exists in the cache.

https://redis-py.readthedocs.io/en/latest/#redis.StrictRedis.zrank

Fixes #25590

thaim/ansible,thaim/ansible