Marks Spreadsheet, when grade cell selected, scrolling up or down modifies grade, which we do not want.

**Description:**

For a Marks Spreadsheet, in the Grades table, when you have a grade cell selected, and you then scroll up using the mouse or arrow key, the grade in that cell will be incremented. Similarly if you did the same with scrolling down, the grade will be decremented. We want to disable this behaviour as graders may encounter this and modify the mark unknowingly.