## Which problem is this PR solving?
Fixes part of jaegertracing#1668

## Description of the changes
Migrates the test for `ChevronDown.tsx` to RTL

## How was this change tested?
Ran the test suite locally

## Checklist
- [X] I have read
https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
- [X] I have signed all commits
- [X] I have added unit tests for the new functionality
- [X] I have run lint and test steps successfully
  - for `jaeger`: `make lint test`
  - for `jaeger-ui`: `yarn lint` and `yarn test`

Signed-off-by: Eshaan Aggarwal <96648934+EshaanAgg@users.noreply.github.com>

Signed-off-by: Eshaan Aggarwal <96648934+EshaanAgg@users.noreply.github.com>

Signed-off-by: Eshaan Aggarwal <96648934+EshaanAgg@users.noreply.github.com>

Signed-off-by: Eshaan Aggarwal <96648934+EshaanAgg@users.noreply.github.com>

Signed-off-by: Eshaan Aggarwal <96648934+EshaanAgg@users.noreply.github.com>