fix: Avoid first time startup costs in tests

[matthewfeickert]

Resolves #14

To avoid startup costs that are associated with the first time the tests are run, run the command once first to make sure everything is setup in the environment

* Run pyhf-validation --version once before test to avoid first run post install startup costs

[codecov]

Codecov Report

Merging #17 (37c4288) into master (e1f4a71) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #17   +/-   ##
=======================================
  Coverage   90.90%   90.90%           
=======================================
  Files           3        3           
  Lines          11       11           
=======================================
  Hits           10       10           
  Misses          1        1           

Flag	Coverage Δ
unittests	90.90% <ø> (ø)

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