Merge branch '5.0' into 5.1

* 5.0:
  Fix abstract method name in PHP doc block
  Various cleanups
  [HttpClient] fix issues in tests
  Fixes sprintf(): Too few arguments in form transformer
  [Console] Fix QuestionHelper::disableStty()
  [Validator] Use Mime component to determine mime type for file validator
  validate subforms in all validation groups
  Update Hungarian translations
  Add meaningful message when Process is not installed (ProcessHelper)
  [PropertyAccess] Fix TypeError parsing again.
  [TwigBridge] fix fallback html-to-txt body converter
  [Security/Http] fix merge
  [ErrorHandler] fix setting $trace to null in FatalError
  [Form] add missing Czech validators translation
  [Validator] add missing Czech translations
  never directly validate Existence (Required/Optional) constraints

Author: nicolas-grekas

Transport/MailgunApiTransport.php

@@ -67,10 +67,10 @@ protected function doSendApi(SentMessage $sentMessage, Email $email, Envelope $e
         $result = $response->toArray(false);
         if (200 !== $response->getStatusCode()) {
             if ('application/json' === $response->getHeaders(false)['content-type'][0]) {
-                throw new HttpTransportException(sprintf('Unable to send an email: '.$result['message'].' (code %d).', $response->getStatusCode()), $response);
+                throw new HttpTransportException('Unable to send an email: '.$result['message'].sprintf(' (code %d).', $response->getStatusCode()), $response);
             }
 
-            throw new HttpTransportException(sprintf('Unable to send an email: '.$response->getContent(false).' (code %d).', $response->getStatusCode()), $response);
+            throw new HttpTransportException('Unable to send an email: '.$response->getContent(false).sprintf(' (code %d).', $response->getStatusCode()), $response);
         }
 
         $sentMessage->setMessageId($result['id']);

Transport/MailgunHttpTransport.php

@@ -69,10 +69,10 @@ protected function doSendHttp(SentMessage $message): ResponseInterface
         $result = $response->toArray(false);
         if (200 !== $response->getStatusCode()) {
             if ('application/json' === $response->getHeaders(false)['content-type'][0]) {
-                throw new HttpTransportException(sprintf('Unable to send an email: '.$result['message'].' (code %d).', $response->getStatusCode()), $response);
+                throw new HttpTransportException('Unable to send an email: '.$result['message'].sprintf(' (code %d).', $response->getStatusCode()), $response);
             }
 
-            throw new HttpTransportException(sprintf('Unable to send an email: '.$response->getContent(false).' (code %d).', $response->getStatusCode()), $response);
+            throw new HttpTransportException('Unable to send an email: '.$response->getContent(false).sprintf(' (code %d).', $response->getStatusCode()), $response);
         }
 
         $message->setMessageId($result['id']);