bug symfony#59836 [Mailer][Postmark] Set CID for attachments when it exists (IssamRaouf)

This PR was squashed before being merged into the 6.4 branch.

Discussion
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[Mailer][Postmark] Set CID for attachments when it exists

| Q             | A
| ------------- | ---
| Branch?       | 6.4  <!-- see below -->
| Bug fix?      | yes
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Issues        | Fix symfony#59819 <!-- prefix each issue number with "Fix #", no need to create an issue if none exists, explain below instead -->
| License       | MIT

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Commits
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83b0491 [Mailer][Postmark] Set CID for attachments when it exists

Author: fabpot

src/Symfony/Component/Mailer/Bridge/Postmark/Transport/PostmarkApiTransport.php

@@ -147,7 +147,7 @@ private function getAttachments(Email $email): array
             ];
 
             if ('inline' === $disposition) {
-                $att['ContentID'] = 'cid:'.$filename;
+                $att['ContentID'] = 'cid:'.($attachment->hasContentId() ? $attachment->getContentId() : $filename);
             }
 
             $attachments[] = $att;