Ensure date is a datetime not just an object

This mostly doesn't even matter but it prevents this warning when adding the delta:

PerformanceWarning: Adding/subtracting object-dtype array to TimedeltaArray not vectorized

pomodoro_to_harvest.py

@@ -78,6 +78,7 @@ timelog["time"] = 30
 # of the day before, so we are, effectively, on West Coast time for determining
 # the day we want to associate a time entry with.  PomodoroPrompt saves as UTC.
 timelog["date"] = timelog["started"].dt.tz_convert("US/Pacific").dt.date
+timelog['date'] = pd.to_datetime(timelog['date'])
 timelog["day_of_week"] = pd.to_datetime(timelog["date"]).dt.day_name()
 
 # If a project has been specified (task prefixed with a colon), then put the