ci: enable gitlint

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.61%. Comparing base (6ee571d) to head (740af0e). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #465 +/- ## ======================================= Coverage 99.61% 99.61% ======================================= Files 53 53 Lines 5493 5493 ======================================= Hits 5472 5472 Misses 21 21 ``` | [Flag](https://app.codecov.io/gh/MozillaSecurity/grizzly/pull/465/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=MozillaSecurity) | Coverage Δ | | |---|---|---| | [](https://app.codecov.io/gh/MozillaSecurity/grizzly/pull/465/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=MozillaSecurity) | `99.61% <ø> (?)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=MozillaSecurity#carryforward-flags-in-the-pull-request-comment) to find out more.

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