Adjust `FindingsFinder` not to depend on dismissal feedback

Adjust https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/finders/security/findings_finder.rb#L87 not to depend on dismissal feedback.

Implementation plan:

• Adjust this https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/finders/security/findings_finder.rb#L87 so that it does not depend on dismissed feedback for the filter (@security_findings ||= include_dismissed? ? all_security_findings : all_security_findings.undismissed). It needs to depend Vulnerability model when feature flag is enabled.