Update rtd config file

[adam-a-a]

Addresses issue:

Summary/Motivation:

Readthedocs check is failing and other checks won't run until the RTD check passes. Let's fix it.

Changes proposed in this PR:

• update config file following Readthedocs config template is broken openedx/edx-cookiecutters#416

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[ksbeattie]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (696dacc) 89.83% compared to head (9c187c1) 89.83%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #220   +/-   ##
=======================================
  Coverage   89.83%   89.83%           
=======================================
  Files          77       77           
  Lines        9307     9307           
=======================================
  Hits         8361     8361           
  Misses        946      946           

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