fix: dont allow course detail page to break editor

[connorhaugh]

At the moment, editors served from V1 libraries are broken because they use the course authoring MFE url (because they use editors in the same way courses do).

This was introduced here: #761

This fix fixes that.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0debaec) 89.69% compared to head (dc2b304) 89.69%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #790   +/-   ##
=======================================
  Coverage   89.69%   89.69%           
=======================================
  Files         503      503           
  Lines        8193     8193           
  Branches     1721     1721           
=======================================
  Hits         7349     7349           
  Misses        817      817           
  Partials       27       27           

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