Fix base64-encoded file uploads not being possible (#12748)

Fix #3804, Fix #5776

spec/controllers/api/proofs_controller_spec.rb

@@ -85,10 +85,7 @@ describe Api::ProofsController do
         end
 
         it 'has the correct avatar url' do
-          first_part = 'https://cb6e6126.ngrok.io/system/accounts/avatars/'
-          last_part  = 'original/avatar.gif'
-
-          expect(body_as_json[:avatar]).to match /#{Regexp.quote(first_part)}(?:\d{3,5}\/){3}#{Regexp.quote(last_part)}/
+          expect(body_as_json[:avatar]).to match "https://cb6e6126.ngrok.io#{alice.avatar.url}"
         end
       end
     end