[2.14] Set ansible_python_interpreter to python3 on debian (fix error with mitogen)

[oomichi]

What type of PR is this?

/kind bug

What this PR does / why we need it:

When mitogen is enable, ubuntu CI fails
This is a backport PR of #6633 for v2.14.

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

@oomichi: PR needs rebase.

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[k8s-ci-robot]

@oomichi: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-kubespray-yamllint	41dcb9f	link	/test pull-kubespray-yamllint

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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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: oomichi
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[oomichi]

Oops, my bad.

/hold