feat(tests): Updated toBeTruthy to toBeDefined in pipeline_charts_spec.js

What does this MR do and why?

• This MR replaces toBeFalsy with toBe(false)
• This MR fixes #369752 (closed)

Screenshots or screen recordings

How to set up and validate locally

1. yarn
2. yarn jest spec/frontend/projects/pipelines/charts/components/pipeline_charts_spec.js

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.