[DependencyInjection] fix @return anno created by PhpDumper
bug #11756 [DependencyInjection] fix @return anno created by PhpDumper (jakubkulhan)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #11756).

Discussion
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[DependencyInjection] fix @return anno created by PhpDumper

| Q             | A
| ------------- | ---
| Fixed tickets | ---
| License       | MIT

If a generated container is inside namespace, generated @return annos are not valid.

Commits
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39c4cc3 [DependencyInjection] fix @return anno created by PhpDumper