Switching Pivot Table column from Date to String throws error.

[aarondr77]

1. Create a pivot table with a datetime column
2. Use the select to change that column to a string column
3. See this error because it is still trying to apply the .dt access to the column.

https://github.com/mito-ds/mito/assets/18709905/3b68d925-d474-4e10-9e2d-343e63c7200c