Fix default S3_HOSTNAME used in mastodon:setup (#19932)

s3-us-east-1.amazonaws.com does not exist.

Co-authored-by: Effy Elden <effy@effy.space>

lib/tasks/mastodon.rake

@@ -194,7 +194,7 @@ namespace :mastodon do
 
           env['S3_HOSTNAME'] = prompt.ask('S3 hostname:') do |q|
             q.required true
-            q.default 's3-us-east-1.amazonaws.com'
+            q.default 's3.us-east-1.amazonaws.com'
             q.modify :strip
           end