Merge branch '7.2' into 7.3

* 7.2:
  remove useless @legacy annotation
  [Mailer] [Transport] Send clone of `RawMessage` instance in `RoundRobinTransport`

Author: nicolas-grekas

src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Transport/MailgunApiTransportTest.php

@@ -98,9 +98,6 @@ public function testCustomHeader()
         $this->assertEquals('amp-html-value', $payload['amp-html']);
     }
 
-    /**
-     * @legacy
-     */
     public function testPrefixHeaderWithH()
     {
         $email = new Email();

src/Symfony/Component/Mailer/Tests/Transport/RoundRobinTransportTest.php

@@ -16,6 +16,8 @@
 use Symfony\Component\Mailer\Exception\TransportExceptionInterface;
 use Symfony\Component\Mailer\Transport\RoundRobinTransport;
 use Symfony\Component\Mailer\Transport\TransportInterface;
+use Symfony\Component\Mime\Header\Headers;
+use Symfony\Component\Mime\Message;
 use Symfony\Component\Mime\RawMessage;
 
 /**
@@ -144,6 +146,27 @@ public function testSendOneDeadAndRecoveryWithinRetryPeriod()
         $this->assertTransports($t, 1, []);
     }
 
+    public function testSendOneDeadMessageAlterationsDoNotPersist()
+    {
+        $t1 = $this->createMock(TransportInterface::class);
+        $t1->expects($this->once())->method('send')
+            ->willReturnCallback(function (Message $message) {
+                $message->getHeaders()->addTextHeader('X-Transport-1', 'value');
+                throw new TransportException();
+            });
+        $t2 = $this->createMock(TransportInterface::class);
+        $t2->expects($this->once())->method('send');
+        $t = new RoundRobinTransport([$t1, $t2]);
+        $p = new \ReflectionProperty($t, 'cursor');
+        $p->setValue($t, 0);
+        $headers = new Headers();
+        $headers->addTextHeader('X-Shared', 'value');
+        $message = new Message($headers);
+        $t->send($message);
+        $this->assertSame($message->getHeaders()->get('X-Shared')->getBody(), 'value');
+        $this->assertFalse($message->getHeaders()->has('X-Transport-1'));
+    }
+
     public function testFailureDebugInformation()
     {
         $t1 = $this->createMock(TransportInterface::class);

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

@@ -50,7 +50,7 @@ public function send(RawMessage $message, ?Envelope $envelope = null): ?SentMess
 
         while ($transport = $this->getNextTransport()) {
             try {
-                return $transport->send($message, $envelope);
+                return $transport->send(clone $message, $envelope);
             } catch (TransportExceptionInterface $e) {
                 $exception ??= new TransportException('All transports failed.');
                 $exception->appendDebug(\sprintf("Transport \"%s\": %s\n", $transport, $e->getDebug()));