enable github sponsor

.github/FUNDING.yml

 # These are supported funding model platforms
 
-github: # Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [user1, user2]
+# Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [user1, user2]
+github: AFLplusplus
 patreon: # Replace with a single Patreon username
 open_collective: AFLplusplusEU
 ko_fi: # Replace with a single Ko-fi username