feat(changelog): containers-deprecated-serverless-containers-v1beta1-dep 2026-07-13 (#6685)

* feat(changelog): add new entry

* Update changelog/july2026/2026-07-13-containers-deprecated-serverless-containers-v1beta1-dep.mdx

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Co-authored-by: Changelog bot <changelog-bot@users.noreply.github.com>
Co-authored-by: vanda-scw <villyes@scaleway.com>