Drop support for Windows 20H2

[torredil]

What is this PR about? / Why do we need it?

As mentioned in the release notes, v1.18.0 is the last minor release of the AWS EBS CSI Driver to support Windows 20H2.

[torredil]

/retest

[ConnorJC3]

/lgtm

I will be approving this after #1597 merges if there is no negative feedback and CI passes.

[ConnorJC3]

/approve

#1597 is in the merge pool

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ConnorJC3

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[ConnorJC3]

/lgtm

[hanyuel]

/lgtm

[k8s-ci-robot]

@torredil: 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-aws-ebs-csi-driver-test-e2e-external-eks-windows	2fa8ad0	link	false	/test pull-aws-ebs-csi-driver-test-e2e-external-eks-windows

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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[ConnorJC3]

/retest