interim notification templates include timestamps in wrong tz

[jennifer-richards]

Describe the issue

In both interim_meeting_cancellation_notice.txt and interim_session_cancellation_notice.txt, the context variables start_time and end_time are interpolated. These should be shown in meeting time. Currently they'll be displayed in settings.TIME_ZONE (aka PST8PDT) instead.

Code of Conduct

• I agree to follow the IETF's Code of Conduct

[jennifer-richards]

Fixed by #4481