Stop checking switcher in docs build

[callumforrester]

We don't want to check switcher because there are 3 possible states for a repo:

1. New project, docs are not published so there is no switcher
2. Existing project with latest skeleton, switcher should be there
3. Existing project with skeleton being either adopted or updated, switcher may or mar not be there and its state is unknown.

Point 3 makes checking switcher difficult, because if it is not as the theme expects, it needs to be manually fixed on every branch.
This PR sets check_switcher to False and adds a comment explaining why.

[codecov]

Codecov Report

Merging #106 (3bc1660) into main (e2e7d86) will not change coverage.
The diff coverage is n/a.

❗ Current head 3bc1660 differs from pull request most recent head e7fcc7d. Consider uploading reports for the commit e7fcc7d to get more accurate results

@@            Coverage Diff            @@
##              main      #106   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines           13        13           
=========================================
  Hits            13        13           

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[coretl]

Please can you squash and push and I'll merge