[SRU] PHP8 compatibility on focal

[ Impact ]

The user is unable to use phpMyAdmin or the related symfony library

[ Test Plan ]

# Reproduced using the 20.04.6 ISO

Run the following commands:

    apt update
    apt upgrade -y
# Install the "add-apt-repository" command
    apt install software-properties-common -y
    add-apt-repository ppa:phpmyadmin/ppa

# Install the deb sury repo
    apt-get -y install lsb-release ca-certificates curl

    curl -sSLo /usr/share/keyrings/deb.sury.org-php.gpg https://packages.sury.org/php/apt.gpg
    sh -c 'echo "deb [signed-by=/usr/share/keyrings/deb.sury.org-php.gpg] https://packages.sury.org/php/ bullseye main" > /etc/apt/sources.list.d/php.list'
    apt update
    apt install php8.2
    apt install mysql-server -y
    service mysql start
# Choose apache2 to auto configure and accept dbcommon setup
    apt install phpmyadmin
    service apache2 start

# Change the root password
    mysql -e "ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password by 'public';"

# Browse: http://localhost/phpmyadmin/
# Login: root/public
# See the error "Unknown parameter $$dbi"

Apply the change in the merge request and login another time, now phpMyAdmin works !

[ Where problems could occur ]

 This exact fix was applied by users for years, there is nothing more to be afraid about.

[ Other Info ]

This has been fixed since jammy.

Recent report at phpMyAdmin: https://github.com/phpmyadmin/phpmyadmin/issues/18498
And the oldest on 20.04.2 LTS: https://github.com/phpmyadmin/phpmyadmin/issues/16968

Fixed by https://code.launchpad.net/~williamdes/ubuntu/+source/symfony/+git/symfony/+merge/442971