audit: ignore unmaintained atty advisory

[aghecenco]

Summary of the PR

cargo audit is currently failing due to this advisory in the (apparently) unmaintained atty crate. Ignoring this specific advisory in order to unblock CI.

Requirements

Before submitting your PR, please make sure you addressed the following requirements:

• [x] All commits in this PR are signed (with git commit -s), and the commit message has max 60 characters for the summary and max 75 characters for each description line.
• [x] All added/changed functionality has a corresponding unit/integration test.
• [x] All added/changed public-facing functionality has entries in the "Upcoming Release" section of CHANGELOG.md (if no such section exists, please create one).
• [x] Any newly added unsafe code is properly documented.

[andreeaflorescu]

We are now ignoring this per repository. Closing this PR.