Small cleanups to URL.join

[bdraco]

#1397 made this a bit less concise, clean it up a bit

[codspeed-hq]

CodSpeed Performance Report

Merging #1416 will not alter performance

_{Comparing join_cleanups (00d0541) with master (e910178)}

Summary

✅ 83 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.06%. Comparing base (e910178) to head (00d0541).
Report is 42 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1416      +/-   ##
==========================================
- Coverage   96.06%   96.06%   -0.01%     
==========================================
  Files          31       31              
  Lines        5770     5762       -8     
  Branches      345      345              
==========================================
- Hits         5543     5535       -8     
  Misses        201      201              
  Partials       26       26              

Flag	Coverage Δ
CI-GHA	96.06% <100.00%> (-0.01%)	⬇️
MyPy	48.58% <93.75%> (-0.08%)	⬇️
OS-Linux	99.55% <100.00%> (-0.05%)	⬇️
OS-Windows	99.61% <100.00%> (-0.01%)	⬇️
OS-macOS	99.30% <100.00%> (-0.01%)	⬇️
Py-3.10.11	99.28% <100.00%> (-0.01%)	⬇️
Py-3.10.15	99.51% <100.00%> (-0.01%)	⬇️
Py-3.11.10	99.51% <100.00%> (-0.01%)	⬇️
Py-3.11.9	99.28% <100.00%> (-0.01%)	⬇️
Py-3.12.7	99.51% <100.00%> (-0.01%)	⬇️
Py-3.13.0	99.51% <100.00%> (-0.01%)	⬇️
Py-3.9.13	99.23% <100.00%> (-0.01%)	⬇️
Py-3.9.20	99.47% <100.00%> (-0.01%)	⬇️
Py-pypy7.3.16	99.52% <100.00%> (-0.01%)	⬇️
Py-pypy7.3.17	99.55% <100.00%> (-0.03%)	⬇️
VM-macos-latest	99.30% <100.00%> (-0.01%)	⬇️
VM-ubuntu-latest	99.55% <100.00%> (-0.05%)	⬇️
VM-windows-latest	99.61% <100.00%> (-0.01%)	⬇️
pytest	99.55% <100.00%> (-0.05%)	⬇️

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