escape $ properly

[Zethson]

Fixes

/opt/hostedtoolcache/Python/3.11.9/x64/lib/python3.11/site-packages/readfcs/_core.py:27: DeprecationWarning: invalid escape sequence '\$'
  if re.match("^\$P\d+[A-Z]$", k)

[github-actions]

🚀 Deployed on https://6633461b163bc4900bcc11d3--readfcs-rpqu.netlify.app

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.23%. Comparing base (0d92033) to head (49a6176).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #37   +/-   ##
=======================================
  Coverage   89.23%   89.23%           
=======================================
  Files           4        4           
  Lines         130      130           
=======================================
  Hits          116      116           
  Misses         14       14           

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