Update contentItems in DefaultImportPage.tsx

Fixes 'Warning: Each child in a list should have a unique "key" prop.'

Signed-off-by: Arturs Jansons <a.jansons@gmail.com>

plugins/catalog-import/src/components/DefaultImportPage/DefaultImportPage.tsx

@@ -39,11 +39,11 @@ export const DefaultImportPage = () => {
   const appTitle = configApi.getOptionalString('app.title') || 'Backstage';
 
   const contentItems = [
-    <Grid item xs={12} md={4} lg={6} xl={8}>
+    <Grid key={0} item xs={12} md={4} lg={6} xl={8}>
       <ImportInfoCard />
     </Grid>,
 
-    <Grid item xs={12} md={8} lg={6} xl={4}>
+    <Grid key={1} item xs={12} md={8} lg={6} xl={4}>
       <ImportStepper />
     </Grid>,
   ];