Drop Julia v1.9

[blegat]

We dropped support for Julia v1.9 in MOI. There is also

Ipopt.jl/README.md

Line 334 in b5b0e62

If you use Ipopt.jl with Julia ≥ v1.9, the linear solver [SPRAL](https://github.com/ralna/spral) is available.

and

Ipopt.jl/README.md

Line 349 in b5b0e62

With Julia v1.9 or later, Ipopt and the linear solvers [MUMPS](https://mumps-solver.org/index.php)

that we could clean up but they could also stay because earlier Julia will make you install older version if Ipopt so it's kind of still true

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b5b0e62) to head (43dd147).

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #551   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines         1192      1192           
=========================================
  Hits          1192      1192           

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