Change custom emoji to be animated when hovering container (#15637)

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/mastodon/components/__tests__/__snapshots__/display_name-test.js.snap

@@ -3,6 +3,8 @@
 exports[`<DisplayName /> renders display name + account name 1`] = `
 <span
   className="display-name"
+  onMouseEnter={[Function]}
+  onMouseLeave={[Function]}
 >
   <bdi>
     <strong