test-browser CI job is extremely flaky

[mourner]

The test-browser Circle CI job fails about 60% of the time in recent days, although it always passes locally. Example failure. Usually it passes one-two tests, then fails with the following error:

unknown error: Chrome failed to start: exited abnormally. (unknown error: DevToolsActivePort file doesn't exist) (The process started from chrome location /usr/bin/google-chrome is no longer running, so ChromeDriver is assuming that Chrome has crashed.)

Sometimes it fails in Firefox rather than Chrome, so it's generally pretty random. It might be related to merging #10367, but I don't see why it would randomly fail as a result of these code changes. Another hypothesis is circleci/node:14.15-browsers circle image having faulty browser set up that crashes easily. 🤷‍♂️

It's really annoying having to restart the failed workflow jobs 2-3 times until it passes before merging a PR, so we should investigate, or in the absense of ideas, temporarily disable the job.

[mourner]

Tried upgrading selenium-webdriver dependency but it didn't help. At this point I'm not sure how to approach this — perhaps it would be best to disable the job until we figure it out. After all, the package is still in alpha, and the tests there are just minimal samples (#9245) which we've never expanded on. cc @kkaefer

[mourner]

Looks like it's running fine now after upgrading the Circle image in #10385.