bug symfony#58025 [Mailer] [Brevo] Support the unique_proxy_open event (richardhj)

This PR was merged into the 6.4 branch.

Discussion
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[Mailer] [Brevo] Support the `unique_proxy_open` event

| 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 #... <!-- prefix each issue number with "Fix #", no need to create an issue if none exists, explain below instead -->
| License       | MIT

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Brevo's webhooks are using an event named `unique_proxy_open`, functionally similiar to the `proxy_open` event.

It is not explicitly mentioned in the Documentation but I log many errors concerning this issue.

<img width="936" alt="Screenshot 2024-08-17 at 01 53 45" src="https://github.com/user-attachments/assets/765d97f7-13bd-4915-960d-0692d823c9b5">

<img width="819" alt="Screenshot 2024-08-17 at 01 56 58" src="https://github.com/user-attachments/assets/daa703ba-b9e3-426c-8c68-60f12fb42acb">

Commits
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1fec2c3 Support the `unique_proxy_open` event

Author: fabpot

src/Symfony/Component/Mailer/Bridge/Brevo/RemoteEvent/BrevoPayloadConverter.php

@@ -41,6 +41,7 @@ public function convert(array $payload): AbstractMailerEvent
                 'unique_opened' => MailerEngagementEvent::OPEN,
                 'opened' => MailerEngagementEvent::OPEN,
                 'proxy_open' => MailerEngagementEvent::OPEN,
+                'unique_proxy_open' => MailerEngagementEvent::OPEN,
                 'complaint' => MailerEngagementEvent::SPAM,
                 default => throw new ParseException(sprintf('Unsupported event "%s".', $payload['event'])),
             };