🌱 Bump go version to v1.21

[Fedosin]

What this PR does / why we need it:

CAPI uses golang v1.21: kubernetes-sigs/cluster-api#9900. We need to do the same.

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 #

[furkatgofurov7]

@Fedosin 👋🏼, CAPI v1.6.X does not use go 1.21 AFAICT https://github.com/kubernetes-sigs/cluster-api/blob/v1.6.0/.golangci.yml#L3, the PR you linked merged into 1.7 milestone

[Fedosin]

@furkatgofurov7 right, in v1.6 they are still on golang v1.20. there is no need to merge this pr right now

[Fedosin]

/hold

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[Fedosin]

/hold cancel

[Fedosin]

/test pull-cluster-api-operator-test-main

[Danil-Grigorev]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Danil-Grigorev

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[furkatgofurov7]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 34a251faa30c3cb1ce43e833c90bd578e6a67e29