Don't create a new URL if fragment unchanged

[asvetlov]

Supersedes #292

Co-Authored-By: Ryan Northey ryan@synca.io

[codecov]

Codecov Report

Merging #384 into master will increase coverage by 0.62%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #384      +/-   ##
========================================
+ Coverage   99.37%   100%   +0.62%     
========================================
  Files           2      2              
  Lines         637    640       +3     
  Branches      145    146       +1     
========================================
+ Hits          633    640       +7     
+ Misses          1      0       -1     
+ Partials        3      0       -3

Impacted Files	Coverage Δ
yarl/__init__.py	100% <100%> (ø)	⬆️
yarl/quoting.py	100% <0%> (+2.4%)	⬆️

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