fix: tolerate searchEndpoint (hashtag) runs in artist description

[grray]

Describe the bug
Since #895, get_artist() raises KeyError for any artist whose description
contains a hashtag:

KeyError: "Unable to find 'urlEndpoint' using path ['navigationEndpoint',
'urlEndpoint', 'url'] on {'clickTrackingParams': '...', 'searchEndpoint':
{'query': '#1billboard', 'params': 'agIoAQ%3D%3D'}}, exception: 'urlEndpoint'"

To Reproduce
YTMusic().get_artist("UCRHts_o65erNP48E0j2qYkw") # Zacardi Cortez
YTMusic().get_artist("UCxFCRsIS2KxYg6LB5OIc4Rw") # Carolyn Arends

Both descriptions contain hashtags ("#1Billboard", "#canadianmusic").

Cause
parse_description_runs() assumes every run with a navigationEndpoint
contains an urlEndpoint, but hashtag runs contain a searchEndpoint instead.

Fix
Resolve the url with nav(..., none_if_absent=True) and fall back to a plain
text run when there is no url. Unit test included.

[sigma67]

Could you please add a test that covers this case?

[grray]

@sigma67 I've added the test. I hope I got everything right.

[sigma67]

Thanks, it seems the failing tests are unrelated, I'll have to look at those separately first