Update Helm release kube-prometheus-stack to v85 (staging)

Author: govuk-ci

charts/kube-prometheus-stack-bootstrap/helm-versions/staging

@@ -1,3 +1,3 @@
 # $repo_url $chart_name: "$chart_version"
-https://prometheus-community.github.io/helm-charts kube-prometheus-stack: "82.18.0"
+https://prometheus-community.github.io/helm-charts kube-prometheus-stack: "85.0.0"
 https://oauth2-proxy.github.io/manifests oauth2-proxy: "10.4.3"