🌱 Bump Cert-manager v1.20.2

[troy0820]

What this PR does / why we need it:

Updates cert-manager to v1.20.2

Prior Art

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes # n/a

/area clusterctl

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[k8s-ci-robot]

@troy0820: 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-apidiff-main	da9b521	link	false	/test pull-cluster-api-apidiff-main

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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