Use HTTP status code constants in security reports specs

The following files uses integer literals for HTTP status codes. For readability, the constants defined in lib/utils/http_status.js should be used instead.

• ee/spec/javascripts/vue_shared/security_reports/grouped_security_reports_app_spec.js
• ee/spec/javascripts/vue_shared/security_reports/split_security_reports_app_spec.js
• ee/spec/javascripts/vue_shared/security_reports/store/actions_spec.js
• ee/spec/frontend/vue_shared/security_reports/store/modules/sast/actions_spec.js