Add --watchAll=false to coverage docs

[ianjmacintosh]

Is your proposal related to a problem?

Yes, when I follow the instructions on https://create-react-app.dev/docs/running-tests/#coverage-reporting to run coverage reporting, I get an empty report. Others have reported this in #6888 #7838 #9322 #9876.

Describe the solution you'd like

Until this changes, I propose updating https://github.com/facebook/create-react-app/blame/master/docusaurus/docs/running-tests.md#L179 to prescribe npm test -- --coverage --watchAll=false

Describe alternatives you've considered

Ideally this behavior would be changed by the Jest team, but jestjs/jest#7331 doesn't seem to have much activity. Maybe there's another issue that's tracking it.

[ianjmacintosh]

I've opened a PR for this, please let me know if this feature request is inappropriate and I'll close it.

[browniefed]

This should be default honestly, very confusing why it defaults to watch in the first place.

[axross]

Just for your information, in my environment, I reproduced the same problem but it outputs the full coverage reports when I manually pass --watchAll with --coverage.

🙅‍♂️ react-scripts test --coverage
🙆‍♂️ react-scripts test --coverage --watchAll