Symfony version(s) affected: 5.3.7, 5.3.8

Description
When the Cache component is configured with a Redis DSN with non-numeric dbindex (eg. redis://redis/foo rather than redis://redis/1), the dbindex is silently ignored.

How to reproduce

<?php
// config/packages/cache.php

use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework) {
    $cache = $framework->cache();

    $cache->app('cache.adapter.redis')
        ->defaultRedisProvider('redis://redis/foo');

    $cache->pool('my_pool.cache')->adapters(['cache.app']);
};

Then start using the cache. Default dbindex 0 will be used.

Possible Solution
Fail or at least log if the DSN contains a dbindex which is not numeric.

Additional context
This line seems to be related:

if (!isset($params['dbindex']) && isset($params['path']) && preg_match('#/(\d+)$#', $params['path'], $m)) {
    …

This condition checks if the dbindex is present (isset($params['path'])) and numeric (preg_match(…)). There's no handling for a present but invalid dbindex.