feat(sca): Add support for malicious package detection

[hcharaf]

Context

We want to see malicious vulnerabilities in the output of ggshield sca scan all

What has been done

1. Updated IncidentSeverity
2. Changed some tests

Validation

PR check list

• [ ] As much as possible, the changes include tests (unit and/or functional)
• [ ] If the changes affect the end user (new feature, behavior change, bug fix) then the PR has a changelog entry (see doc/dev/getting-started.md). If the changes do not affect the end user, then the skip-changelog label has been added to the PR.

[FlorianPerucki]

Looking good! Tested locally: