function gussExtension return wrong result, return csv instead of right answer "txt" or "text"

[lanxiuying]

Direction
function gussExtension return wrong result, return csv instead of right answer "txt" or "text";

Describe the bug
when txt,text files uploaded

   if ($filelist = $this->request->getFiles()) {
                   var_dump($file->guessExtension());//return csv instead text
       }

**why this happend** **because $mime['csv'] include 'text/plain' in file "application\Config\Mimes.php"，so function always return csv when the input is ‘text/plain’**

public static function guessExtensionFromType(string $type = ‘text/plain’){  
		$type = trim(strtolower($type), '. ');  
		foreach (self::$mimes as $ext => $types)  
		{  
			if (is_string($types) && $types == $type)  
			{  
				return $ext;  
			}  
			else if (is_array($types) && in_array($type, $types))  
			{  
				return $ext;  
			}  
		}  
		return null;  
	}`  

CodeIgniter 4 version
CodeIgniter 4 Development

Affected module(s)
system\Files
system\Files\File.php
application\Config\Mimes.php
Expected behavior, and steps to reproduce if appropriate
return file's correct mimetype
Context

• OS: [e.g. Windows 7]
• Web server [e.g. Apache 2.4]
• PHP version [7.1] with module php_fileinfo active

[MGatner]

MIMES is in app/ intentionally (I presume) to encourage user updates, so feel free to edit it. MIMES are checked in the order they are listed in that config so if you want .txt to return text/plain you can move it higher. Since guessExtensionFromType is explicitly just matching off extension there is no way to differentiate between CSV and TXT, short of removing text/plain from the CSV list (which would be fine to do as well, if you prefer).