fix: LxmlLinkExtractor unique_list missing key

[jxlil]

Added key argument to unique_list in LxmlLinkExtractor

Before:

seenkey: Link(url='http://example.com/page1', text='Página 1', fragment='', nofollow=False)

After:

seenkey: http://example.com/page1

Closes #3273

[codecov]

Codecov Report

Merging #6221 (5e51417) into master (1c9d308) will increase coverage by 0.04%.
Report is 68 commits behind head on master.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6221      +/-   ##
==========================================
+ Coverage   88.55%   88.60%   +0.04%     
==========================================
  Files         160      161       +1     
  Lines       11607    11775     +168     
  Branches     1883     1908      +25     
==========================================
+ Hits        10279    10433     +154     
- Misses       1003     1011       +8     
- Partials      325      331       +6     

Files	Coverage Δ
scrapy/linkextractors/lxmlhtml.py	95.55% <100.00%> (ø)

... and 9 files with indirect coverage changes

[Gallaecio]

Can you add a test for it?

[jxlil]

I think that in tests/test_linkextractors.py all cases are already being covered. On codecov.io it also seems that this change is covered: https://app.codecov.io/gh/scrapy/scrapy/pull/6221

[Gallaecio]

If this was properly covered, the tests would have failed before the change. Let me give it a go later on.

[jxlil]

Hi @Gallaecio I see that you added some tests (some were also added here: #6232)

Is there something missing that I can help with?

[Gallaecio]

Oh, right, I forgot to approve 🤦

cc @wRAR

[jxlil]

Oh ok, no problem. Thanks!

[jxlil]

Hi @wRAR ,

Hope you're doing well. Are any additional changes needed in this PR? Thank you.

[wRAR]

@jxlil this is still in my backlog, I hope to revisit it soon :)

[wRAR]

Thanks!