Symfony gc_probability on debian

[maximecolin]

By default, Symfony set gc_probability to 1 and override php ini. On debian with sury php, a cron job clean the session instead of php session garbage collector. So we need to set gc_probability to ~ to tell Symfony to not override the default php config (0).

framework:
    session:
        # Don't override php gc_probability config
        gc_probability: ~