fix(auth): ensures / is URL encoded in sources auth environment variables (fix #3169)

[noirbizarre]

Pull Request Checklist

• A news fragment is added in news/ describing what is new.
• Test cases added for changed code.

Describe what you have changed in this PR.

/ was not URL encoded because urllib.parse.quote exclude it by default (targeting querystrings).
This PR ensures it is.
(I'll submit a Python urllib.parse.quote documentation PR too as it says it is safe for path by default, which is not, only in querystring)

Fixes #3169

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.20%. Comparing base (ff9e871) to head (852f697).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3170   +/-   ##
=======================================
  Coverage   86.20%   86.20%           
=======================================
  Files         107      107           
  Lines       10715    10715           
  Branches     2292     2292           
=======================================
  Hits         9237     9237           
  Misses       1015     1015           
  Partials      463      463           

Flag	Coverage Δ
unittests	86.00% <100.00%> (ø)

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