There was only one different line between these two lines, and we really
want these two files to be as similar as possible, so testing on a
staging server we get the same results we'll get on production.
This duplication made it easy to forget to update the staging.rb file
when updating the production.rb, particularly when upgrading to a new
version of Rails, which automatically changes the production.rb file but
not the staging.rb one.
So, now that we're getting ready to upgrade to Rails 7.0, we're basing
the staging configuration on the production one, just like we based the
preproduction configuration on the staging one in commit 7b91adb16.
b5b03e4496