Added call to validate() in fit_model()

[eacharles]

Problem & Solution Description (including issue #)

Code Quality

• My code follows the code style of this project
• I have written unit tests or justified all instances of #pragma: no cover; in the case of a bugfix, a new test that breaks as a result of the bug has been added
• My code contains relevant comments and necessary documentation for future maintainers; the change is reflected in applicable demos/tutorials (with output cleared!) and added/updated docstrings use the NumPy docstring format
• Any breaking changes, described above, are accompanied by backwards compatibility and deprecation warnings

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.00%. Comparing base (1fe979b) to head (0b543b5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #218   +/-   ##
=======================================
  Coverage   99.00%   99.00%           
=======================================
  Files          47       47           
  Lines        3432     3432           
=======================================
  Hits         3398     3398           
  Misses         34       34           

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