Add test for inbound policy index deletion

[adleong]

PR https://github.com/linkerd/linkerd2/pull/12088 fixed an issue where removing and then re-adding certain policy resources could leave the policy index in an incorrect state. We add a test for the specific condition that triggered this behavior to prevent against future regressions.

Verified that this test fails prior to https://github.com/linkerd/linkerd2/pull/12088 but passes on main.