Update m_helper.fpp

[sbryngelson]

Fixes a doxygen bug (hopefully).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 43.66%. Comparing base (93a1aac) to head (d2696e9).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #808   +/-   ##
=======================================
  Coverage   43.66%   43.66%           
=======================================
  Files          65       65           
  Lines       19159    19159           
  Branches     2338     2338           
=======================================
  Hits         8365     8365           
  Misses       9370     9370           
  Partials     1424     1424           

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