Fix frontend tests

spec/frontend/artifacts_settings/components/__snapshots__/keep_latest_artifact_checkbox_spec.js.snap

@@ -7,7 +7,6 @@ exports[`Keep latest artifact checkbox when application keep latest artifact set
   <b-form-checkbox-stub
     checked="true"
     class="gl-form-checkbox"
-    plain="true"
     value="true"
   >
     <strong

spec/frontend/monitoring/components/duplicate_dashboard_form_spec.js

@@ -23,7 +23,7 @@ describe('DuplicateDashboardForm', () => {
     findByRef(ref).setValue(val);
   };
   const setChecked = (value) => {
-    const input = wrapper.find(`.form-check-input[value="${value}"]`);
+    const input = wrapper.find(`.custom-control-input[value="${value}"]`);
     input.element.checked = true;
     input.trigger('click');
     input.trigger('change');