x/website: Some pages cannot display video

[180909]

What is the URL of the page with the issue?

https://go.dev/blog/waza-talk
https://go.dev/blog/two-recent-go-talks

What is your user agent?

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.159 Safari/537.36

Screenshot

[gopherbot]

Change https://golang.org/cl/348249 mentions this issue: fix video can't display