fix: Handle Parsel > 1.7.0 warning

[Laerte]

resolves: #5903

Please let me know if this is the best approach to handle this.

[codecov]

Codecov Report

Merging #5918 (8501d64) into master (ea15ff1) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 8501d64 differs from pull request most recent head 7317ff1. Consider uploading reports for the commit 7317ff1 to get more accurate results

@@           Coverage Diff           @@
##           master    #5918   +/-   ##
=======================================
  Coverage   88.81%   88.81%           
=======================================
  Files         162      162           
  Lines       11181    11184    +3     
  Branches     1818     1819    +1     
=======================================
+ Hits         9930     9933    +3     
  Misses        965      965           
  Partials      286      286           

Impacted Files	Coverage Δ
scrapy/selector/unified.py	100.00% <100.00%> (ø)

[wRAR]

Thanks!
We can address the potential optimization improvements separately, together with already filed #5906.