fix: time series chart labeling

[briangregoryholmes]

Fixes a regression from #8633 where dates were being improperly converted back into a time zone for display purposes.

Following up another PR to ensure we have test coverage for this surface

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!