chore(t8s-cluster/dependencies): update docker.io/bitnami/kubectl docker tag to v1.28.4

[renovate]

This PR contains the following updates:

Package	Update	Change
docker.io/bitnami/kubectl	patch	1.28.2 -> 1.28.4

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[teutonet-bot]

🤖 I have diffed this beep boop

"/$namespace/$kind/$name.yaml" for normal resources
"/$namespace/HelmRelease/$name/$namespace/$kind/$name.yaml" for HelmReleases <- this is recursive
'null' means it's either cluster-scoped or it's in the default namespace for the HelmRelease

charts/t8s-cluster/ci/artifacthub-values.yaml

charts/t8s-cluster/ci/cidrs-values.yaml

charts/t8s-cluster/ci/injectedCertificateAuthorities-values.yaml

charts/t8s-cluster/ci/securityGroups-values.yaml

charts/t8s-cluster/ci/calico-values.yaml

charts/t8s-cluster/ci/bastion-values.yaml

charts/t8s-cluster/values.yaml

charts/t8s-cluster/ci/gpu-flavor-values.yaml has no changes