fix: use unit timezone when parsing scheduled appointment datetime

[rogeriolino]

Issue: novosga/novosga#454

Related to novosga/novosga#492

Summary

• Fix DateTime::createFromFormat call that ignored the unit's configured timezone when building a DateTime from a scheduled appointment's date+time strings
• Without this fix, appointments in units with a non-default timezone could be incorrectly flagged as expired at triage

Test plan

• Confirm a scheduled appointment in a unit with a non-UTC timezone
• Verify the appointment is not incorrectly rejected as expired at triage

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