DM-33942: Use a negative integer for test universe

[timj]

We currently cache universes based on version integer so we
need to use a version number that does not clash with any
possible real universe.

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Merging #246 (596145a) into main (590c34a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #246   +/-   ##
=======================================
  Coverage   72.14%   72.14%           
=======================================
  Files          60       60           
  Lines        6628     6628           
  Branches     1250     1250           
=======================================
  Hits         4782     4782           
  Misses       1621     1621           
  Partials      225      225           

Impacted Files	Coverage Δ
tests/test_quantumGraph.py	94.85% <ø> (ø)

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[timj]

Closed by #248