Better anchor URL for include reference

[alamirault]

Hello,

When a ref is in a included file which is used multiple time, generated anchor it's always the same and not the best.

I created a phpunit reproducer. Problem was found on https://github.com/symfony/symfony-docs/pull/18791#discussion_r1307678134

The reproducer branch, has also a second commit, which "fix" the behavior. Please, tell me if I can open a PR, or if there is a better alternative