execute tests with the full range of supported Mailer component releases

The conflict rule does not exclude the 5.4, 6.0 and 6.1 releases of the Mailer component. So we
should make sure that we also run tests against these versions.

Author: xabbuh

composer.json

@@ -47,7 +47,7 @@
         "symfony/html-sanitizer": "^6.1",
         "symfony/http-client": "^5.4|^6.0",
         "symfony/lock": "^5.4|^6.0",
-        "symfony/mailer": "^6.2",
+        "symfony/mailer": "^5.4|^6.0",
         "symfony/messenger": "^6.1",
         "symfony/mime": "^5.4|^6.0",
         "symfony/notifier": "^5.4|^6.0",