compatibility-versions-feature-gate-test has a bug currently where retroactively making code a GA feature to deprecate it is not handled

[aaron-prindle]

What happened:
I am seeing a new test failure with the compat version feature gate test:

https://testgrid.k8s.io/sig-testing-kind#compatibility-versions-feature-gate-test

FAIL: unexpected feature 'LegacySidecarContainers' found in /metrics, got=1

Occurred recently between these commits:
kubernetes/kubernetes@75909b8...fbdf890

I believe it is related to this PR:
kubernetes/kubernetes@f2f4634

Relevant snippet:

pkg/features/versioned_kube_features.go

LegacySidecarContainers: {
        {Version: version.MustParse("1.0"), Default: true, PreRelease: featuregate.GA},
        {Version: version.MustParse("1.33"), Default: false, PreRelease: featuregate.Deprecated},
    },

This feature gate is WAI and the test itself needs to handle the case where a pre-existing feature/codepath (that has no prior feature gate) becomes a deprecated gate. In this case there is a retroactive GA feature gate added as a "hack". This case is not accounted for currently in the test

What you expected to happen:
I expected test to pass

How to reproduce it (as minimally and precisely as possible):
See posted test grid logs and run for repro case

Please provide links to example occurrences, if any:

Anything else we need to know?:

[aaron-prindle]

/sig api-machinery
/assign