Use new CSS selector in dashboard specs

This is a temporary fix as using css classes to target
elements in tests is flaky. We will need to find a proper
solution once we have fix this problem.

app/assets/javascripts/monitoring/components/dashboard_panel.vue

@@ -374,7 +374,6 @@ export default {
       :graph-data="graphData"
       v-bind="$attrs"
       v-on="$listeners"
-      class="js-basic-chart"
     />
     <component
       :is="timeSeriesChartComponent"

ee/spec/features/clusters/cluster_health_dashboard_spec.rb

@@ -78,7 +78,7 @@ describe 'Cluster Health board', :js, :kubeclient, :use_clean_rails_memory_store
         expect(page).to have_css('.prometheus-graph')
         expect(page).to have_css('.prometheus-graph-title')
         expect(page).to have_css('[_echarts_instance_]')
-        expect(page).to have_css('.js-basic-chart')
+        expect(page).to have_css('.gl-legend-inline')
       end
     end