Add compatibility with PHP 8.1

[julienloizelet]

No description provided.

[julienloizelet]

At first, we have a PHPUNIT error, so we have update phpunit version to a more 8.1 compatible version : it seems that 8.5.21 is good enough.

Once this done, there is an issue with symfony/cache during unit test :
TypeError: Memcached::setMulti(): Argument #2 ($expiration) must be of type int, int given

It seems that the initial issue is due to memcached itself : php-memcached-dev/php-memcached#496 and that we have to wait for a new release. (the last release was done in 2019)

See also cakephp/cakephp#15534

[julienloizelet]

Here is the error thrown by github action unit tests : https://github.com/julienloizelet/php-cs-bouncer/runs/4555869742?check_suite_focus=true

For some reason, this error is thrown when using tests github actions and ddev local unit test but not when using the local script tests-local-php8.1.sh

[julienloizelet]

For information, we are waiting for a 8.1 compatible release of php-memcached : php-memcached-dev/php-memcached#495

[julienloizelet]

At this moment, the last release memcached (3.1.5) is not compatible with php 8.1 and there is no schedule for a new release.

Considering this, we will just exclude any Memcached test during Unit test using something like :

if (PHP_VERSION_ID >= 80100 && version_compare(phpversion('memcached'), '3.1.5', '<=')) {
    // do not use Memcached
}

[julienloizelet]

Closed : #59