[Finder] fixed typehint of the Finder::addAdapter() method
minor #10835 Finder typehint fix (hhamon)

This PR was merged into the 2.3 branch.

Discussion
----------

Finder typehint fix

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

Commits
-------

f3b0ef1 [Finder] fixed typehint of the Finder::addAdapter() method