Do not reload the Jupytext config file unless a notebook is opened/saved

[mwouts]

Closes #797

[codecov]

Codecov Report

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@@           Coverage Diff           @@
##             main     #860   +/-   ##
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  Coverage        ?   99.06%           
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  Files           ?      111           
  Lines           ?    10525           
  Branches        ?        0           
=======================================
  Hits            ?    10427           
  Misses          ?       98           
  Partials        ?        0           

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