minor #20046 [HttpClient] send necessary HTTP headers (xabbuh)

This PR was merged into the 5.4 branch.

Discussion
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[HttpClient] send necessary HTTP headers

see symfony/symfony#57742

Commits
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e4bfad3 send necessary HTTP headers

Author: javiereguiluz

http_client.rst

@@ -676,6 +676,7 @@ when the streams are large)::
     $client->request('POST', 'https://...', [
         // ...
         'body' => $formData->bodyToString(),
+        'headers' => $formData->getPreparedHeaders()->toArray(),
     ]);
 
 If you need to add a custom HTTP header to the upload, you can do::