Mailer rename .txt to .txt.php (#3842)

* Mailer rename .txt to .txt.php

app/Mailers/UserMailer.php

@@ -5,7 +5,7 @@
  */
 class FreshRSS_User_Mailer extends Minz_Mailer {
 	public function send_email_need_validation($username, $user_config) {
-		$this->view->_path('user_mailer/email_need_validation.txt');
+		$this->view->_path('user_mailer/email_need_validation.txt.php');
 
 		$this->view->username = $username;
 		$this->view->site_title = FreshRSS_Context::$system_conf->title;

lib/Minz/Mailer.php

@@ -14,7 +14,7 @@ use PHPMailer\PHPMailer\Exception;
  * with, for instance:
  *
  * ```
- * $this->view->_path('user_mailer/email_need_validation.txt')
+ * $this->view->_path('user_mailer/email_need_validation.txt.php')
  * ```
  *
  * Minz_Mailer uses the PHPMailer library under the hood. The latter requires