fix(docs-infra): add spacing between past and future events sections (#40881)

This commit adds some more spacing between the past and future events
sections on the "Events" page.

Before: ![events spacing before][1]
After: ![events spacing after][2]

[1]: https://user-images.githubusercontent.com/8604205/107989711-82eca580-6fdb-11eb-837e-1255d439d51a.png
[2]: https://user-images.githubusercontent.com/8604205/107989708-81bb7880-6fdb-11eb-8cf4-4653254e1c37.png

PR Close #40881

aio/src/app/custom-elements/events/events.component.html

@@ -27,6 +27,8 @@
   </tbody>
 </table>
 
+<br />
+
 <h2>Where we already presented:</h2>
 <table class="is-full-width">
   <thead>
@@ -47,4 +49,4 @@
       </td>
     </tr>
   </tbody>
-</table>
+</table>