Fix: Switch to using ascii lowercase to avoid gurobi bug

[codecov[bot]]

Codecov Report

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

Project coverage is 95.01%. Comparing base (a7cd271) to head (d995d65).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #59 +/- ## ======================================= Coverage 95.01% 95.01% ======================================= Files 13 13 Lines 1384 1384 ======================================= Hits 1315 1315 Misses 69 69 ``` | [Flag](https://app.codecov.io/gh/Bravos-Power/pyoframe/pull/59/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Bravos-Power) | Coverage Δ | | |---|---|---| | [smart-tests](https://app.codecov.io/gh/Bravos-Power/pyoframe/pull/59/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Bravos-Power) | `95.01% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Bravos-Power#carryforward-flags-in-the-pull-request-comment) to find out more.

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