[ci] Don't erroneously mark failures as successes

Randomly noticed this when I looked at a recent [DevTools regression test run](https://github.com/facebook/react/actions/runs/13578385011).

I don't recall why we added `continue-on-error` previously, but I believe it was to keep all jobs in the matrix running even if one were to fail, in order to fully identify any failures from code changes like build or test failures.

There is now a `fail-fast` option which does this. [`continue-on-error`](https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for-github-actions#jobsjob_idcontinue-on-error) now means:

> Prevents a workflow run from failing when a job fails. Set to true to allow a workflow run to pass when this job fails.

so it's not correct to use it.