Backport of UI: Stabilize KV secret tests into release/1.12.x

[hc-github-team-secure-vault-core]

Backport

This PR is auto-generated from #20491 to be assessed for backporting due to the inclusion of the label backport/1.12.x.

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The below text is copied from the body of the original PR.

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Test failures on the 1.11 branch were failing seemingly due to a KV engine having existing secrets, and the list items that the test was looking for were bumped off the page in tests. This change ensures that each KV mount is deleted after the test is finished.

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Overview of commits

• d1c9318

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