ci: make format required (devs should run make format before committing) (openai#1979)

Author: filintod

.github/workflows/tests.yml

@@ -22,6 +22,8 @@ jobs:
  enable-cache: true
  - name: Install dependencies
  run: make sync
+ - name: Verify formatting
+ run: make format-check
  - name: Run lint
  run: make lint