Update validate_script.py to check for circular workflow graphs

[ilaflott]

Describe your changes

Issue ticket number and link (if applicable)

Fixes #XXX (replace XXX with the issue number and GitHub will autolink the PR to the issue)

Checklist before requesting a review

• I ran my code
• I tried to make my code readable
• I tried to comment my code
• I wrote a new test, if applicable
• I wrote new instructions/documentation, if applicable
• I ran pytest and inspected it's output
• I ran pylint and attempted to implement some of it's feedback
• No print statements; all user-facing info uses logging module

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.09%. Comparing base (ad94447) to head (22f6603).

Files with missing lines	Patch %	Lines
fre/pp/validate_script.py	0.00%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (60.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #940   +/-   ##
=======================================
  Coverage   82.09%   82.09%           
=======================================
  Files          67       67           
  Lines        3736     3736           
=======================================
  Hits         3067     3067           
  Misses        669      669           

Flag	Coverage Δ
unittests	82.09% <0.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
fre/pp/validate_script.py	18.18% <0.00%> (ø)

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