Cast the Redis port to int

Cast the Redis port to int

The `Redis::connect()` method expects the `$port` parameter to be an integer.
PHP will automatically cast numeric strings to an integer, but error out with
an TypeError if the string is not a well-formed number. This TypeError will not
be caught in an `catch(\Exception $e)` block, because TypeError does not
inherit Exception.

Perform an explicit cast to ensure the fallback to DiskCacheSource works.