Fix composer.json file for the Symfony Mailer module name to symfony_mailer

First of all. Thanks for maintaining this module
Currently in the process of switching from the deprecated Swift Mailer module replaced by Symfony Mailer

Problem/Motivation

The Symfony Mailer's composer.json file look like:

{
  "name": "drupal/symfony-mailer",
  "description": "Symfony Mailer",
  "type": "drupal-module",
  "license": "GPL-2.0-or-later",
  "require": {
    "html2text/html2text": "^4.0.1",
    "symfony/mailer": "^5.3.0",
    "tijsverkoyen/css-to-inline-styles": "^2.2"
  }
}

Proposed resolution

Change "name": "drupal/symfony-mailer", to "name": "drupal/symfony_mailer",

Remaining tasks

• Fix patch/MR
• Review
• Commit
• Release

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A