Fix: Remove signature change of middleware

[glensc]

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Description

The middleware must be void, not return things.

Reverts breakage from bbd3606

Checklist

• This change adds test coverage for new/changed/fixed functionality
• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not the default branch

[glensc]

Could the maintainers here:

1. create atomic commits, not monstrous commits like bbd3606 that changed many things at once
2. maintainers also create pull requests to have review and reasoning explained with the changes.

I think this is already 3rd problem reported by that same commit.

[glensc]

@jfromaniello another fix to a breaking change

[glensc]

can this be revieved and merged and released?