ci: temporary disable preview theme workflow

[qwerty541]

Related to https://github.com/anuraghazra/github-readme-stats/issues/3404. @rickstaa We recently discussed on discord addition of one gradient theme per maintainer and subsequent disabling preview theme workflow. So feel free to merge this pull request when your theme will be ready or if you don't want to add it.

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Name	Status	Preview	Updated (UTC)
github-readme-stats	✅ Ready (Inspect)	Visit Preview	Nov 30, 2023 7:09pm

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (1656ec6) 98.02% compared to head (54f5be1) 98.02%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3514   +/-   ##
=======================================
  Coverage   98.02%   98.02%           
=======================================
  Files          27       27           
  Lines        6267     6267           
  Branches      549      549           
=======================================
  Hits         6143     6143           
  Misses        121      121           
  Partials        3        3           

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