test: add failing test case for res.redirect(undefined) ref #6941

[Wisp-xd]

This PR adds a test case to reproduce the issue described in #6941.

When passing undefined to res.redirect():

1. It prints a express deprecated warning to the console.
2. But it still sends a 302 response with an invalid Location: undefined header, instead of throwing an error.

This test expects a 500 error, so it currently FAILS, confirming the unexpected behavior.

Ref: #6941