docs: mark Snyk Code as not supported

[lili2311]

• [ ] Tests written and linted ℹ︎
• [x] Documentation written ℹ︎
• [ ] Commit history is tidy ℹ︎

What this does

Mark Snyk Code as not supported, since there is no snyk monitor functionality for it in the CLI

[aarlaud]

:tada: This PR is included in version 1.8.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: