Rollup merge of #151692 - GuillaumeGomez:reduce-flaky, r=jieyouxu

Try to reduce rustdoc GUI tests flakyness

Should help with rust-lang/rust#93784.

I replaced a use of `puppeteer.wait` function with a loop instead (like the rest of `browser-ui-test`).

r? @jieyouxu

Author: Zalathar