chore: remove cross-fetch

[2ndalpha]

Stopped using cross-fetch.
Now NodeJS has built-in support for fetch (I bumped the minimum required version to 18).

Unfortunately we still need cross-fetch in tests.
See jsdom/jsdom#1724

Checklist

• Code is covered with tests.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.31%. Comparing base (5ffcb60) to head (afa5115).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #722      +/-   ##
==========================================
- Coverage   82.36%   82.31%   -0.05%     
==========================================
  Files          23       23              
  Lines         788      786       -2     
  Branches      136      137       +1     
==========================================
- Hits          649      647       -2     
+ Misses        138      130       -8     
- Partials        1        9       +8     

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[raluik]

• Let's update the Node version in other GitHub workflows as well.