Fix Epic timeline bar misalignment when start date is in last timeframe month and end date is out of range

What does this MR do?

Fixes timeline bar misalignment for Epic in Roadmap where start date of Epic falls within last month of timeframe and end date is out of range

Screenshots

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] Documentation created/updated
• [ ] API support added
• Tests added for this feature/bug
• Review
  • [ ] Has been reviewed by UX
  • Has been reviewed by Frontend
  • [ ] Has been reviewed by Backend
  • [ ] Has been reviewed by Database
• EE specific content should be in the top level /ee folder
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• [ ] Internationalization required/considered
• [ ] If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• [ ] End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #5658 (closed)