.webm is concatenated to the end of my outtmpl after update in embedded script

[Methodiconion]

Checklist

• I'm reporting a broken site support issue
• [x ] I've verified that I'm running youtube-dl version 2020.09.14
• [x ] I've checked that all provided URLs are alive and playable in a browser
• [ x] I've checked that all URLs and arguments with special characters are properly quoted or escaped
• [ x] I've searched the bugtracker for similar bug reports including closed ones
• [ x] I've read bugs section in FAQ

Verbose log

PASTE VERBOSE LOG HERE

Description

Hey, so I've been using the inbuilt ysearch feature for a while now, and I haven't changed my code which was working fine until update.

options={"outtmpl":"SOMETHING.mp4"}

Despite setting my filename to .mp4, I end up with a file "SOMETHING.mp4.webm". I'm not sure why this would happen, but it momentarily broke my script. It's not like it's a big deal (I just found it by os.listdir(), and I was deleting the file anyway), but it's definitely weird, and I suppose it constitutes a bug, even though the module didn't crash or anything.

Incidentally, I'm fine with adding a verbose log in the event that would actually help you to fix this, but otherwise it doesn't seem like the kind of thing which needs one.