adds failing test case for non-catchable pattern in requirements

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
| License       | MIT
| Doc PR        | none

If you have a non-catchable pattern in requirements like f.e. a positive lookahead (``.+(?=/foo/)``), the generator will not accept the parameter as the parameter itself cannot fulfil the requirement, but only matches in the context of the entire path.

I'm not sure how/if you would like to fix this, this only adds a failing test case. One way might be to generate the URL and run the matcher against the entire URL.

/cc @Tobion