Raise minimum iminuit version after next iminuit release

[alexander-held]

There is a small bug in the (current) latest iminuit 2.2.1, leading to the wrong EDM display after HESSE. This was fixed in scikit-hep/iminuit#599, should raise minimum iminuit version to include this fix after the next iminuit release.

update: v2.3.0 has been released

related: #156

[alexander-held]

This would also be resolved by scikit-hep/pyhf#1306, which raises the requirement via pyhf to v2.4.0.

[alexander-held]

pyhf now pins to iminuit~=2.1,<2.4 via scikit-hep/pyhf#1307, which will be resolved to 2.3.0 in a new installation. Could now either leave it at that, or add a minimum of 2.3.0 in cabinetry.

[alexander-held]

cabinetry will not add an additional requirement of iminuit~=2.3 in #156. The issue described above is not breaking any basic functionality, and users will now receive version 2.3 anyway in a fresh installation after #156. This avoids any complication of having to add an additional upper version limit to stay in line with pyhf, which in the future will presumably be removed again or increased to a higher minimum version requirement.