chore(deps): update dependency symfony/mailer to v8 (#83)

Co-authored-by: mailersend-renovate[bot] <197618458+mailersend-renovate[bot]@users.noreply.github.com>
Co-authored-by: Peter Ocansey <ocanseypeter@gmail.com>

Author: mailersend-renovate[bot]

composer.json

@@ -26,7 +26,7 @@
         "mailersend/mailersend": "^0.36.0",
         "nyholm/psr7": "^1.5",
         "php-http/guzzle7-adapter": "^1.0",
-        "symfony/mailer": "^6.0 || ^7.0"
+        "symfony/mailer": "^6.0 || ^7.0 || ^8.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^9.0 || ^10.5 || ^12.0",