Fix #288: remove deprecated 'model' property in tests.

[anevolbap]

Closes issue #288.

Removes the FutureWarning in tests caused by a deprecated property:

FutureWarning: Model.model property is deprecated. Just use Model.
    warnings.warn("Model.model property is deprecated. Just use Model.", FutureWarning)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.50%. Comparing base (67d9e0e) to head (60e537c).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #291   +/-   ##
=======================================
  Coverage   76.50%   76.50%           
=======================================
  Files          20       20           
  Lines        1345     1345           
=======================================
  Hits         1029     1029           
  Misses        316      316           

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[drbenvincent]

Thanks!