Avoid a redirect

Co-Authored-By: NXavier Fernandez <xav.fernandez@gmail.com>

.github/FUNDING.yml

@@ -7,4 +7,4 @@ community_bridge: # Replace with a single Community Bridge project-name e.g., cl
 liberapay: # Replace with a single Liberapay username
 issuehunt: # Replace with a single IssueHunt username
 otechie: # Replace with a single Otechie username
-custom: https://pypi.org/sponsor # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']
+custom: "https://pypi.org/sponsor/" # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']