If you proxy your site through Cloudflare and turn on Cloudflare analytics, its default behavior appears to be to automatically add the JS tag for you in HTML responses [1] (you can also disable that and manually add the tag to your HTML)

They provide a lot of this type of thing - rewriting HTML responses with optimizations "at the edge" instead of you doing it at your origin.

[1] https://developers.cloudflare.com/analytics/web-analytics/ge...