Resolve "Broken master: karma test failing in spec/javascripts/boards/components/issue_due_date_spec.js"

What does this MR do?

In some cases date.setDate(date.getDate() + 17); will result in the new date being in the next year. This might cause failing tests (depending on today's date) since the component will then use the format mmm d, yyyy for rendering the date (as opposed to mmm d for formatting dates within the current year).

This MR fixes the karma test in order to test this component logic.

/cc @andr3

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/55402

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer

Closes #55402 (closed)