Regression tests to highlight #242

[tomascohen]

@jhthorsen I'm not entirely sure about this regression tests, but they highlight some weird behavior. Particularly, the first one is adding extra spaces in suspicious ways. And the second call is stripping the trailing occurences of the header.

Count on me if I can be of help.

[jhthorsen]

• https://github.com/jhthorsen/mojolicious-plugin-openapi/issues/150
• https://github.com/jhthorsen/mojolicious-plugin-openapi/commit/6594e9ec0fd3c53386b1785d68969c3b9c3d3b2a