[C#] feat: add ActionPlanner unit test (#1160)

## Linked issues

#minor: partial of #1116 

## Details

Provide a list of your changes here. If you are fixing a bug, please
provide steps to reproduce the bug.

#### Change details

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appropriate

**code snippets**:

**screenshots**:

## Attestation Checklist

- [ ] My code follows the style guidelines of this project

- I have checked for/fixed spelling, linting, and other errors
- I have commented my code for clarity
- I have made corresponding changes to the documentation (we use
[TypeDoc](https://typedoc.org/) to document our code)
- My changes generate no new warnings
- I have added tests that validates my changes, and provides sufficient
test coverage. I have tested with:
  - Local testing
  - E2E testing in Teams
- New and existing unit tests pass locally with my changes

### Additional information

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