[release-0.11] 🌱 Remove mdbooth as a maintainer

[k8s-infra-cherrypick-robot]

This is an automated cherry-pick of #2760

/assign k8s-infra-cherrypick-robot

[netlify]

✅ Deploy Preview for kubernetes-sigs-cluster-api-openstack ready!

Name	Link
🔨 Latest commit	09ba64e
🔍 Latest deploy log	https://app.netlify.com/projects/kubernetes-sigs-cluster-api-openstack/deploys/68e8ab93790994000742d5b0
😎 Deploy Preview	https://deploy-preview-2770--kubernetes-sigs-cluster-api-openstack.netlify.app
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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[k8s-ci-robot]

@k8s-infra-cherrypick-robot: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-provider-openstack-test	09ba64e	link	true	/test pull-cluster-api-provider-openstack-test

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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