bug symfony#59256 [Mailer] Fix Sendmail memory leak (rch7)

This PR was merged into the 6.4 branch.

Discussion
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[Mailer] Fix Sendmail memory leak

| 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#50486 <!-- prefix each issue number with "Fix #", no need to create an issue if none exists, explain below instead -->
| License       | MIT

Previous PR: symfony#59239

Fixes issue symfony#50486 (Sendmail transport runs out of memory).
- I have removed unrelated changes that somehow got in the previous attempt of pull request because of wrong base version.
- As for the "metrics about the memory leak itself" - it is in the issue 50486. When write(), which is defined in vendor/symfony/mailer/Transport/Smtp/Stream/AbstractStream.php, is called without $debug parameter, it's true by default, and $this->debug gets appended all the email body data incrementally.
  So for example if you have loop sending personalized emails to 200,000 subscribers 20 kB each, $this->debug becomes 4 GB, plus overhead, and the script runs out of resources.
  The fix eliminates the problem.
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Commits
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c74e2a3 fix_50486 - memory leak

Author: nicolas-grekas

src/Symfony/Component/Mailer/Transport/SendmailTransport.php

@@ -114,7 +114,7 @@ protected function doSend(SentMessage $message): void
         $this->stream->setCommand($command);
         $this->stream->initialize();
         foreach ($chunks as $chunk) {
-            $this->stream->write($chunk);
+            $this->stream->write($chunk, false);
         }
         $this->stream->flush();
         $this->stream->terminate();