XML cube output fails for numpy < 2.3

[ukmo-ccbunney]

🐛 Bug Report

Changes made in #6518 result in cube.xml() failing for numpy versions < 2.3

How To Reproduce

With HEAD of Iris main and numpy==2.2.6:

from iris.cube import Cube
import numpy as np

print(np.__version__)

cube = Cube(data=np.ones(10), standard_name='air_pressure')
print(cube.xml())

Error message:

  File ".../python3.12/site-packages/numpy/_core/arrayprint.py", line 361, in get_printoptions
    opts['legacy'] = {
                     ^
KeyError: '2.2'

Expected behaviour

Shouldn't error.
Looks like some defensive conditionals are needed for checking numpy version?

Environment

numpy==2.2.6