Drop Node 18 support

[flevi29]

Pull Request

What does this PR do?

• removes all Node.js 18 references, adapts code to version 20
  • Node.js 18 is about to enter End Of Life period, so it's time to drop support: https://github.com/nodejs/Release?tab=readme-ov-file#release-schedule

Token generation and aborting requests might stop working for Node.js 18 users.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.01%. Comparing base (7da269f) to head (b19b464).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1927      +/-   ##
==========================================
- Coverage   99.02%   99.01%   -0.01%     
==========================================
  Files          18       18              
  Lines        1435     1424      -11     
  Branches      303      299       -4     
==========================================
- Hits         1421     1410      -11     
  Misses         14       14              

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