doc: fix ambasador markdown list

PR-URL: nodejs#55361
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

doc/contributing/advocacy-ambasador-program.md

@@ -45,9 +45,9 @@ If there is no objection within 14 days, the nomination is approved.
 
 To onboard an ambassador, a member of the TSC will:
 
-* \[] Add the ambassador to the nodejs/ambassadors team.
-* \[] Add the ambassador to the nodejs/ambassadors `README.md`.
-* \[] Add the ambassador to the OpenJS Slack channel.
+* \[ ] Add the ambassador to the nodejs/ambassadors team.
+* \[ ] Add the ambassador to the nodejs/ambassadors `README.md`.
+* \[ ] Add the ambassador to the OpenJS Slack channel.
 
 ## Reviewing content