[release-1.6] 🌱 Makefile: pin controller-gen binary to go 1.21

[chrischdi]

What this PR does / why we need it:

Bumping to go 1.22 in kubekins broke controller-gen < 0.14.0 because of incompatibility to go >= 1.22

This pins compiling controller-gen to 1.21.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
xref: #10813

/area devtools

[chrischdi]

/assign @sbueringer
/assign @fabriziopandini

[killianmuldoon]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 96924a2234f9a9b04e92edf169162db4b5d83e5d

[sbueringer]

Very clean! Nice

/approve

For now let's just use this on a case-by-case basis whenever we need it. Eventually I want to have binary releases of controller-gen / setup-envtest so we can just download the binary instead of compiling it ourselves all the time.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sbueringer

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[chrischdi]

/cherry-pick release-1.5

[k8s-infra-cherrypick-robot]

@chrischdi: new pull request created: #10945

In response to this:

/cherry-pick release-1.5

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