DM-36237: Pass through http proxy variables to tests.

[erykoff]

This allows scons tests to run on USDF and other locations that need proxies to connect to the internet for tests that it (including anything with astropy.time).

[codecov]

Codecov Report

Base: 19.73% // Head: 19.73% // No change to project coverage 👍

Coverage data is based on head (2a1998c) compared to base (940f518).
Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #112   +/-   ##
=======================================
  Coverage   19.73%   19.73%           
=======================================
  Files          18       18           
  Lines        1956     1956           
  Branches      519      519           
=======================================
  Hits          386      386           
  Misses       1536     1536           
  Partials       34       34           

Impacted Files	Coverage Δ
python/lsst/sconsUtils/tests.py	11.11% <0.00%> (ø)

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[timj]

Don't worry about the code coverage. I think we need to work out how to have code coverage for the scons command itself that runs the tests.