Resolve "API call to retrieve information of wrong token returns error "400" instead of "401""

What does this MR do and why?

Fixes #347319 (closed)

Since we were overriding Doorkeeper::Oauth::TokenInfoController, we lost the changes that were pushed upstream in the doorkeeper via https://github.com/doorkeeper-gem/doorkeeper/pull/1202, which is the reason why this bug came into existence.

To make sure we are in sync with the upstream changes, we make changes in our overridden controller as per the upstream change, which fixes the problem.

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