Bump swiftmailer/swiftmailer from 5.4.12 to 6.2.3

Bumps [swiftmailer/swiftmailer](https://github.com/swiftmailer/swiftmailer) from 5.4.12 to 6.2.3.
- [Release notes](https://github.com/swiftmailer/swiftmailer/releases)
- [Changelog](https://github.com/swiftmailer/swiftmailer/blob/master/CHANGES)
- [Commits](swiftmailer/swiftmailer@v5.4.12...v6.2.3)

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composer.json

@@ -31,7 +31,7 @@
   "require": {
     "php": ">=7.3.0",
     "phpseclib/phpseclib": "~2.0",
-    "swiftmailer/swiftmailer": "~5.0",
+    "swiftmailer/swiftmailer": "~6.2",
     "erusev/parsedown": "~1.0",
     "erusev/parsedown-extra": "~0.8.1",
     "tecnickcom/tcpdf": "~6.0",