PHP Fatal error: Uncaught PDOException: could not find driver

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$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 22.04.1 LTS
Release:	22.04
Codename:	jammy
~$ docker-compose -v
docker-compose version 1.29.2, build unknown
++ cat docker-compose.yml
services:
    web:
        build: .
        ports:
            - 8000:80
        volumes:
            - ./dbconnect:/var/www/html/dbconnect
    db:
        image: mysql
        environment:
            MYSQL_DATABASE: tdb
            MYSQL_ROOT_PASSWORD: tpass
++ cat Dockerfile
FROM php:apache
RUN docker-php-ext-install pdo_mysql
++ cat dbconnect
mysql:dbname=tdb;host=db
++ cat main
#!/usr/bin/php
<?php
new PDO($argv[1], "root", "tpass");
++ ./main 'mysql:dbname=tdb;host=db'
PHP Fatal error:  Uncaught PDOException: could not find driver in

Why?