Dockerfile.php-base: Remove php7.4-luasandbox package

The following error started happening during image building:

Reading package lists...
Reading package lists...
Building dependency tree...
Reading state information...
ca-certificates is already the newest version (20200601~deb10u2).
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
php7.4-luasandbox : Depends: phpapi-20180731
E: Unable to correct problems, you have held broken packages.
The command '/bin/sh -c DEBIAN_FRONTEND=noninteractive apt-get update && apt-get install -y --no-install-recommends memcached ca-certificates php7.4-cli php7.4-bcmath php7.4-bz2 php7.4-curl php7.4-dba php7.4-gd php7.4-gmp php7.4-intl php7.4-mbstring php7.4-mysql php7.4-xml php7.4-excimer php7.4-apcu php7.4-geoip php7.4-igbinary php7.4-memcached php7.4-msgpack php7.4-redis php7.4-fpm wmf-certificates php7.4-excimer php7.4-luasandbox php7.4-wikidiff2 php7.4-wmerrors php7.4-yaml' returned a non-zero code: 100

so I removed the offending package from the list and now builds work again.