Symfony version(s) affected: 4.4.21

Description
The cache:pool:clear command does not delete any keys when using a Redis connection with prefix set.

How to reproduce

I'm using the Redis extension as the cache.adapter.redis adapter's connection and setting a prefix on the Redis class with the following services.yaml lines:

    #REDIS
    Redis:
        class: Redis
        lazy: true
        calls:
            -   method: connect
                arguments:
                    - '%redis_host%'      # host: string. can be a host, or the path to a unix domain socket.
                    - '%redis_port%'      # port:  int, optional
                    - 0                   # float, value in seconds (optional, default is 0 meaning unlimited)
                    - null                # reserved: should be NULL if retry_interval is specified
                    - 200                 # retry_interval: int, value in milliseconds (optional)
                    - 0                   # read_timeout: float, value in seconds (optional, default is 0 meaning unlimited)
            -   method: setOption
                arguments:
                    - !php/const Redis::OPT_PREFIX
                    - '%env(APP_ENV)%_store:'

This makes the Redis prefixed in production like 'prod_store'. The cache is created and writes just fine in that namespace, but when trying to clear a specific cache using cache:pool:clear command or all of them with cache:pool:clear cache.global_clearer , the cache remains intact without changes.

Possible Solution
I believe the issue is that here in the RedisTrait the line that scans for cache keys to delete:

$host->scan($cursor, $namespace.'*', 1000)

This generates the following redis command:

"SCAN" "0" "COUNT" "1000" "MATCH" "tdYoyvcfPq:*"

which doesn't honor the prefix so it finds no matches. It would have to be something like

$host->scan($cursor, $host->_prefix($namespace.'*'), 1000)

which would create

"SCAN" "0" "COUNT" "1000" "MATCH" "prod_store:tdYoyvcfPq:*"

Additional context

Ultimately this is because the Redis class is a little strange in how it handles prefixes. It automatically adds them for set and deleting functions, but not on scans. There is actually a mention of this in a phpredis/phpredis issue.

Then again maybe I missed a symfony config value somewhere that I'm supposed to set 😏

If this is a legit bug, I'd be happy to take a crack and submit a pull request fix.