Bump the dev-dependencies group with 5 updates

Bumps the dev-dependencies group with 5 updates:

| Package | From | To |
| --- | --- | --- |
| [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) | `8.5.33` | `9.6.15` |
| [phpmailer/phpmailer](https://github.com/PHPMailer/PHPMailer) | `6.8.0` | `6.9.1` |
| [vlucas/phpdotenv](https://github.com/vlucas/phpdotenv) | `5.5.0` | `5.6.0` |
| [dealerdirect/phpcodesniffer-composer-installer](https://github.com/Dealerdirect/phpcodesniffer-composer-installer) | `0.7.2` | `1.0.0` |
| [wp-coding-standards/wpcs](https://github.com/WordPress/WordPress-Coding-Standards) | `2.3.0` | `3.0.1` |


Updates `phpunit/phpunit` from 8.5.33 to 9.6.15
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/9.6.15/ChangeLog-9.6.md)
- [Commits](sebastianbergmann/phpunit@8.5.33...9.6.15)

Updates `phpmailer/phpmailer` from 6.8.0 to 6.9.1
- [Release notes](https://github.com/PHPMailer/PHPMailer/releases)
- [Changelog](https://github.com/PHPMailer/PHPMailer/blob/master/changelog.md)
- [Commits](PHPMailer/PHPMailer@v6.8.0...v6.9.1)

Updates `vlucas/phpdotenv` from 5.5.0 to 5.6.0
- [Release notes](https://github.com/vlucas/phpdotenv/releases)
- [Commits](vlucas/phpdotenv@v5.5.0...v5.6.0)

Updates `dealerdirect/phpcodesniffer-composer-installer` from 0.7.2 to 1.0.0
- [Release notes](https://github.com/Dealerdirect/phpcodesniffer-composer-installer/releases)
- [Changelog](https://github.com/PHPCSStandards/composer-installer/blob/main/.github_changelog_generator)
- [Commits](PHPCSStandards/composer-installer@v0.7.2...v1.0.0)

Updates `wp-coding-standards/wpcs` from 2.3.0 to 3.0.1
- [Release notes](https://github.com/WordPress/WordPress-Coding-Standards/releases)
- [Changelog](https://github.com/WordPress/WordPress-Coding-Standards/blob/develop/CHANGELOG.md)
- [Commits](WordPress/WordPress-Coding-Standards@2.3.0...3.0.1)

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-type: direct:development
  update-type: version-update:semver-major
  dependency-group: dev-dependencies
- dependency-name: phpmailer/phpmailer
  dependency-type: direct:development
  update-type: version-update:semver-minor
  dependency-group: dev-dependencies
- dependency-name: vlucas/phpdotenv
  dependency-type: direct:development
  update-type: version-update:semver-minor
  dependency-group: dev-dependencies
- dependency-name: dealerdirect/phpcodesniffer-composer-installer
  dependency-type: direct:development
  update-type: version-update:semver-major
  dependency-group: dev-dependencies
- dependency-name: wp-coding-standards/wpcs
  dependency-type: direct:development
  update-type: version-update:semver-major
  dependency-group: dev-dependencies
...

Signed-off-by: dependabot[bot] <support@github.com>

composer.json

@@ -7,10 +7,10 @@
 		]
     },
 	"require-dev": {
-		"phpunit/phpunit": "^8",
+		"phpunit/phpunit": "^9",
 		"phpmailer/phpmailer": "^6",
 		"vlucas/phpdotenv": "^5.2",
-		"dealerdirect/phpcodesniffer-composer-installer": "^0.7.1",
+		"dealerdirect/phpcodesniffer-composer-installer": "^1.0.0",
 		"wp-coding-standards/wpcs": "*"
 	},
 	"config": {