Fix documentation link for upgrading PostgreSQL

lib/gitlab/database.rb

@@ -147,7 +147,7 @@ module Gitlab
           is required for this version of GitLab.
           <% if Rails.env.development? || Rails.env.test? %>
           If using gitlab-development-kit, please find the relevant steps here:
-            https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/master/doc/howto/postgresql.md#upgrade-postgresql
+            https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/postgresql.md#upgrade-postgresql
           <% end %>
           Please upgrade your environment to a supported PostgreSQL version, see
           https://docs.gitlab.com/ee/install/requirements.html#database for details.