Check if the new L-BFGS-B algorithm in scipy 1.15 is generally less precise or our test case was an exception

[janosg]

In #555 we had to reduce the precision of a test case due to the new L-BFGS-B implementation in scipy 1.15; We should run a full benchmark or at least create a self-contained small example that shows the difference before we reach out to scipy maintainers. The test case here is not small enough because it uses optimagic constraints.