fix(perf): Add missing key prop in SampleInfo Block component (#68216)

the `time_spent_percentage` percentage block did not have a `key` prop,
resulting in a console error message from React:


![image](https://github.com/getsentry/sentry/assets/16740047/02262e86-32da-4994-9904-44747a598b20)

Author: 0Calories

static/app/views/starfish/views/spanSummaryPage/sampleList/sampleInfo/index.tsx

@@ -86,7 +86,7 @@ function SampleInfo(props: Props) {
         );
       case 'time_spent_percentage()':
         return (
-          <Block title={DataTitles.timeSpent} alignment="left">
+          <Block key={metric} title={DataTitles.timeSpent} alignment="left">
             <TimeSpentCell
               containerProps={{style}}
               percentage={spanMetrics?.[`time_spent_percentage()`]}