Create Test Cases for one cell with preq cells, and an alt cell that has a duplicate formula as the original

[colelloa]

          Wondering how this behaves when prerequisite cells are present in the if part of the loop. 
          The same fix may need to be applied to it as well? Needs to be checked with new test cases.

_Originally posted by @erdogmush in https://github.com/cmusv/pysheetgrader-core/pull/36#discussion_r1072944507_

From discussion on https://github.com/cmusv/pysheetgrader-core/pull/36

Add test case that would sum together the score in a cell with duplicate alt cells and some prereq - should cover line 45 on formula.py: https://github.com/cmusv/pysheetgrader-core/blob/main/pysheetgrader/grading/strategy/formula.py#L45