fix(charts): update helm release victoria-metrics-k8s-stack to v0.25.8

[renovate[bot]]

This PR contains the following updates:

Package	Update	Change
victoria-metrics-k8s-stack	patch	0.25.7 -> 0.25.8

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Release Notes

VictoriaMetrics/helm-charts (victoria-metrics-k8s-stack)

### [`v0.25.8`](https://togithub.com/VictoriaMetrics/helm-charts/releases/tag/victoria-metrics-k8s-stack-0.25.8) ### Release notes for version 0.25.8 **Release date:** 2024-08-30   - fixed external notifiers rendering, when alertmanager is disabled. See [this issue](https://togithub.com/VictoriaMetrics/helm-charts/issues/1378)

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