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Clean up kublet secret and configmap unit test

**What this PR does / why we need it**:

These changes are clean-up items to fix confusing code encountered while investigating #52043. No actual bugs are fixed here (except, maybe, correcting unit tests that had actual/expected swapped).

A summary of the changes, as listed in the commit:

* Expected value comes before actual value in assert.Equal()
* Use `assert.Equal()` instead of `assert.True()` when possible
* Add a unit test that verifies no-op pod updates to the `secret_manager` and the `configmap_manager`
* Add a clarifying comment about why it's good to seemingly delete a secret on updates.
* Fix (for now, non-buggy) variable shadowing issue

**Special notes for your reviewer**:

N/A

**Release note**:
```release-note
NONE
```