Update privatek8s AKS cluster to Kubernetes 1.26

previews of *.jenkins.io pull requests (infra.ci.jenkins.io) infra.ci.jenkins.io release.ci.jenkins.io www.jenkins.io

[Final Message] The operation finished with success at 09:15am UTC

[Initial Message] We’re doing an AKS cluster upgrade from 1.25 to 1.26 the Tuesday 07th of November 2023, starting at 08:00am UTC.

The expected impacts are:

• infra.ci.jenkins.io will be down during 20 to 30 min (time for the upgrade to be performed and persistent volumes to be migrated)
• No website preview of *.jenkins.io on pull requests
• release.ci.jenkins.io will be down during 20 to 30 min (time for the upgrade to be performed and persistent volumes to be migrated)