[OptimizationMOI] fix compat bounds in Project.toml

[odow]

Checklist

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

Additional context

x-ref: https://discourse.julialang.org/t/ac-optimal-power-flow-in-various-nonlinear-optimization-frameworks/78486/88?u=odow

I haven't tested locally, so let's see what CI says.

Ipopt_jll is a test-only dependency. I also added some missing compat bounds. MOI requires Julia 1.6, so the lower Julia bound is now also 1.6.

[codecov[bot]]

Codecov Report

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

Comparison is base (6f193a3) 1.68% compared to head (8690bfd) 8.69%. Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #705 +/- ## ========================================= + Coverage 1.68% 8.69% +7.00% ========================================= Files 31 31 Lines 2491 2496 +5 ========================================= + Hits 42 217 +175 + Misses 2449 2279 -170 ```

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