Fix validation method regarding MIME type keys

Merged Gosia Ksionek requested to merge fix_bug_with_mime_types into master

What does this MR do?

In https://gitlab.com/gitlab-org/security/gitlab/-/merge_requests/1450 I introduced new validation. This MR is limiting this validation to apply only to usernames that end with dot and MIME type.

Related issues: #335278 (closed)

Screenshots or Screencasts (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

  • Label as security and @ mention @gitlab-com/gl-security/appsec
  • The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
  • Security reports checked/validated by a reviewer from the AppSec team
Edited by Gosia Ksionek