Add encode in keys command to fix the support with django-redis-4.9.0

[jbagot]

Since django-redis has been updated to 4.9.0 is using CacheKey object like a pattern for the keys command. This caused an error in this line: pattern = pattern.decode('utf-8').
Then if before this line we can add the pattern = self._encode(pattern) we can avoid this. Also if the pattern is a normal string like the default '*' works.