Fix mail attachs tcmime *** (#4229)

When the file name consists of alphanumeric characters, it is normal to receive the attachment name.
However，However, problems will occur if the file name is changed to Chinese.
This has nothing to do with the file type

scrapy/mail.py

@@ -73,8 +73,7 @@ class MailSender(object):
                 part = MIMEBase(*mimetype.split('/'))
                 part.set_payload(f.read())
                 Encoders.encode_base64(part)
-                part.add_header('Content-Disposition', 'attachment; filename="%s"' \
-                    % attach_name)
+                part.add_header('Content-Disposition', 'attachment', filename=attach_name)
                 msg.attach(part)
         else:
             msg.set_payload(body)