Fix Redis session tests

Requirements:

1. Please set php version to 7.2
2. Make sure that the redis PHP extension is also installed. If not installed (e.g. on Ubuntu/Linuxmint):

   sudo apt install -y php-redis

   sudo service apache2 restart

Test

1. Spin up a redis server:

   docker run --name my-redis --network host -d redis

2. Edit your config.php to add:

   define('TEST_SESSION_REDIS_HOST', '127.0.0.1');

3. Run phpunit on the redis sessions:

   ./vendor/bin/phpunit lib/tests/session_redis_test.php

   1. Confirm pass (not skip)
4. Run a full phpunit run without process isolation:

   ./vendor/bin/phpunit

   1. Confirm pass of entire suite