Proto: fix coq:lint error ignoring message

Context

This MR is there to fix the coq:lint error in the CI. This error is non-fatal but annoying as the CI is not green anymore. We do so by ignoring the current error messages.

Manually testing the MR

Check that the CI is green (and not orange).

Checklist

• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR