I don't believe there is a way to lock it. But if you really want to clear the comments, you can use the API to recurse and delete all the comments--this is a quick Nodejs snip from Bing Chat with Octokit: https://gist.github.com/extremeheat/1042a8a933f0987b265a70d4...

I just deleted it. I'll figure out what to do with all of the emails about all of the comments later. Probably something fun with sentiment analysis and large language models.

You can't for GitHub Gists :(.