move playground loading indicator image (#21816)

components/playground/editor/LoadingIndicator.tsx

@@ -3,7 +3,7 @@ import { Box, Text } from '@primer/components'
 export function LoadingIndicator() {
   return (
     <Box display="flex" flexDirection="column" alignItems="center" py={4}>
-      <img width="120px" src="/playground/loading.gif" alt="bouncing octocat" />
+      <img width="120px" src="/assets/images/playground/loading.gif" alt="bouncing octocat" />
       <Text fontFamily="mono" fontSize={1} color="gray.8">
         Loading...
       </Text>