Bump kubectl to 1.30.1

[wokoman]

What this PR does / why we need it:
kubectl on the provided URI doesn't use git tag, but actual Kubernetes version. Meaning trying to download 0.21.0 yields 404.

Special notes for your reviewer:
Some places used kubectl in version 1.26.1, but Dockerfile was stuck on 1.21.0 for some reason. Thus the Dockerfile couldn't be built, as suggested here in docs. I bumped it to latest.

PR Readiness Checklist:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.56%. Comparing base (4ee7d5e) to head (2f30f55).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #453   +/-   ##
=======================================
  Coverage   86.56%   86.56%           
=======================================
  Files          23       23           
  Lines         856      856           
=======================================
  Hits          741      741           
  Misses        115      115           

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[jkroepke]

Thanks!