[Routing] Add test to validate that default value is allowed to not match requirement

[tcoch]

Q	A
Branch?	6.4
Bug fix?	no
New feature?	no
Deprecations?	no
Issues	#61022
License	MIT

Suppose you have this route definition:

$route = new Route('/test/{foo}', ['foo' => 'foo-'], ['foo' => '\w+'], []);

With this route definition:

• /test/foo works
• /test/foo- fails, because the dash is not permitted by the requirement
• /test works, thanks to the default value. However, the value of the parameter foo does not meet the requirement.

[nicolas-grekas]

Thank you @tcoch.