Add return type required by Symfony

[nlighteneddesign]

Description

This add a missing return type expected by Symfony.

Manual testing steps

I need this MR so I can test in my CI
I will review the rest later.

Issues

• VendorExposeCommand execute is missing a return type. #82

Pull request checklist

• The target branch is correct
  • See picking the right version
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• The commit messages follow our commit message guidelines
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• Code changes follow our coding conventions
• This change is covered with tests (or tests aren't necessary for this change)
• Any relevant User Help/Developer documentation is updated; for impactful changes, information is added to the changelog for the intended release
• CI is green

[emteknetnz]

We can't merge this as because a method signature change is a breaking change, so we'd need to release a new major version (3.0.0) in order to do this.

[nlighteneddesign]

I'm not sure why you'd close this, whether you need a new version or not the next version of console requires the return type so this will eventually need to be updated.