Build SDF from source to reproduce test failures

[chapulina]

• 1a1baf7: Reproduce the broken tests we're seeing on Garden in Bumps in garden: use ign-math7 and dependents #1264
• 67f735a: Testing the potential fix on SDF's

[scpeters]

I was able to reproduce the test failure using nightly debs and a matching gzdev branch name in #1265 (comment)

[codecov]

Codecov Report

Merging #1266 (67f735a) into ign-gazebo6 (fe335f9) will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           ign-gazebo6    #1266   +/-   ##
============================================
  Coverage        61.97%   61.97%           
============================================
  Files              276      276           
  Lines            23000    23000           
============================================
  Hits             14254    14254           
  Misses            8746     8746           

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[chapulina]

Confirmed failures and fixes with GitHub actions for the 2 commits above:

• 1a1baf7: https://github.com/ignitionrobotics/ign-gazebo/runs/4668996334?check_suite_focus=true
• 67f735a: https://github.com/ignitionrobotics/ign-gazebo/runs/4669021230?check_suite_focus=true