[CI] Fix "ESLint & Flow & Jest" workflow.

Summary:
Experienced the same isue described in https://linear.app/comm/issue/ENG-2505/investigate-why-buildkite-ci-didnt-pick-up-eslint-issues

with the following: https://buildkite.com/comm/eslint-and-flow-and-jest/builds/4877#018552b3-4a50-487d-8e70-c6fd7d8c9e65

where issues were logged but workflows didn't fail: https://blob.sh/e7ff64.png

Test Plan: local testing to make sure errors are deterministically caught

Reviewers: tomek, marcin, varun, ginsu

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D6038