FDG-11153 Improve Code Coverage - multichart-renderer.ts

[LaKeishaW]

JIRA Ticket:

FDG-11153

The following are ALL required for the PR to be merged:

• Provided testing instructions in JIRA ticket if applicable
• Provided mocks or additional information in JIRA ticket if applicable
• Verified cross-browser compatibility: Chrome, Safari, Firefox, Edge
• Verified mobile/tablet/desktop/monitor responsiveness
• Verified that this PR does not create any new accessibility issues (via Axe Chrome)
• Verify all files are covered by at least 93% test coverage if applicable
• Verify that dashes are used for any visible defaults of evergreen values if applicable
• Check for code quality
  + Watch out for irrelevant changes
  + Take time to understand the logic and flow; be on guard for pitfalls
  + Look at handoff between components (esp. number of props)
  + Watch out for literals (vs. variables) for css specs if applicable

[github-actions]

Total Line Coverage: 93.08% ✅