Improved detection of content-type for .fail files (#5711)

* Fix for file extension of .fail files.
The `Content-Type` header may contain a charset, which cause XML and JSON .fail files to have a .html extension.

* If a REST API outputs text/plain content, the .fail file should have the .txt extension.

Author: jasny

src/Codeception/Lib/InnerBrowser.php

@@ -67,13 +67,19 @@ public function _failed(TestInterface $test, $fail)
         }
         $filename = preg_replace('~\W~', '.', Descriptor::getTestSignatureUnique($test));
 
-        $extensions = ['application/json' => 'json', 'text/xml' => 'xml', 'application/xml' => 'xml'];
+        $extensions = [
+            'application/json' => 'json',
+            'text/xml' => 'xml',
+            'application/xml' => 'xml',
+            'text/plain' => 'txt'
+        ];
 
         $internalResponse = $this->client->getInternalResponse();
 
-        $responseContentType = $internalResponse ? $internalResponse->getHeader('content-type') : null;
+        $responseContentType = $internalResponse ? $internalResponse->getHeader('content-type') : '';
+        list($responseMimeType) = explode(';', $responseContentType);
 
-        $extension = isset($extensions[$responseContentType]) ? $extensions[$responseContentType] : 'html';
+        $extension = isset($extensions[$responseMimeType]) ? $extensions[$responseMimeType] : 'html';
 
         $filename = mb_strcut($filename, 0, 244, 'utf-8') . '.fail.' . $extension;
         $this->_savePageSource($report = codecept_output_dir() . $filename);