KEP-3619: Fix the directory name for KEP-3619 beta blog post

[everpeace]

Description

#50792 set its publish date and remove draft: true from the front matter. However, the directory name still contains XXXX-XX-XX. This PR updates the directory name.

Although I'm not sure about it, I expected this PR will NOT change its already published blog URL: https://kubernetes.io/blog/2025/05/06/kubernetes-v1-33-fine-grained-supplementalgroups-control-beta/.

Updated: Preview URL shows it does not seem to be changed.
https://deploy-preview-50823--kubernetes-io-main-staging.netlify.app/blog/2025/05/06/kubernetes-v1-33-fine-grained-supplementalgroups-control-beta/

Issue

ref: https://github.com/kubernetes/website/pull/50792/files#r2077399519

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[rytswd]

Sorry I missed this earlier... Thanks for the catch!
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: rytswd
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[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 34378ffe43ae1d1836788ba607173697d4993863

[rytswd]

My understanding is that this change is more for the blog markdown sanity, which makes it easy for SIG Docs Blog team to manage the old articles easily. As you pointed out with the preview build, I do not think this would actually affect the already-published blog 👍

[everpeace]

/assign @natalisucks

[rytswd]

CC @lmktfy