Fix return phpdoc
minor #12985 [HttpFoundation] Fix return phpdoc (Koc)

This PR was merged into the 2.3 branch.

Discussion
----------

[HttpFoundation] Fix return phpdoc

| Q             | A
| ------------- | ---
| Bug fix?      | tiny (for IDE autocompletion)
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

What about using `self` or `static` keyword for this?

Commits
-------

9af2d81 Fix return phpdoc