[ard] Reduce strictness of url regular expression

[olifre]

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Description of your pull request and other information

The - is optional, and fails to match for example:
https://www.daserste.de/unterhaltung/serie/in-aller-freundschaft-die-jungen-aerzte/videos/diversity-tag-sanam-afrashteh100.html
Use -? to accept also URLs without - before the trailing part.

[pukkandan]

https://www.daserste.de/unterhaltung/serie/in-aller-freundschaft-die-jungen-aerzte/videos/diversity-tag-sanam-afrashteh100.html

Maybe consider adding this as a test case

[olifre]

Maybe consider adding this as a test case

I surely can do that, but the link will be expired in ~1 year, since the content is only kept for one year. Is this still a useful test case?

[pukkandan]

You can add it like this:

{
    'url': 'https://www.daserste.de/unterhaltung/serie/in-aller-freundschaft-die-jungen-aerzte/videos/diversity-tag-sanam-afrashteh100.html',
    'only_matching': True,
}, 

That way only the regex is tested, not the download

[olifre]

@pukkandan Many thanks, this was not clear to me (my first youtube-dl PR). I added the test in the second commit :-).