Puma 6.4.1 causing increased errors

Summary

Puma was upgraded to 6.4.1 in !140922 (merged). This caused an increase in errors (gitlab-com/gl-infra/production#17372 (closed)) and was subsequently reverted in !141409 (merged), which caused the errors to stop. Puma should remain on version 6.4.0 until https://github.com/puma/puma/issues/3313 is addressed upstream.