🌱 test: use cluster without worker definition for kcp only test

[chrischdi]

What this PR does / why we need it:

We had a nil pointer which was fixed via #11197

This PR increases test-coverage by using a cluster without having any workers defined.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

/area e2e-testing

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