test: fix typo in variable name

[AayushSabharwal]

Checklist

• [ ] Appropriate tests were added
• [ ] Any code changes were done in a way that does not break public API
• [ ] All documentation related to code changes were updated
• [ ] The new code follows the contributor guidelines, in particular the SciML Style Guide and COLPRAC.
• [ ] Any new documentation only uses public API

Additional context

Add any other context about the problem here.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 28.98%. Comparing base (2f1cd8d) to head (54aa0b9).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #705 +/- ## ========================================== - Coverage 31.47% 28.98% -2.49% ========================================== Files 55 55 Lines 4588 4581 -7 ========================================== - Hits 1444 1328 -116 - Misses 3144 3253 +109 ```

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