Error when writing two-dimensional signal in mrcz format

[nem1234]

Describe the bug

When writing 2-dimensional signal in mrcz format,
IndexError exception is raised in rsciio/mrcz/api.py.

>   pixelsize = [signal["axes"][I]["scale"] for I in _WRITE_ORDER]
E   IndexError: list index out of range

To Reproduce

Steps to reproduce the behavior:

from hyperspy.signals import Signal2D

s = Signal2D(np.arange(256, dtype=np.uint8).reshape(16,16))
s.save("test.mrcz")

Expected behavior

current mrcz/specifications.yaml shows
writes: [[2, 0], [2, 1], [2, 2], [3, 0]]
but it seems that only 3-dimensional data can be accepted.
writes should be [[3, 0]] ?

Python environement:

• RosettaSciIO version: main/HEAD
• Python version: 3.8
• HyperSpy version: RELEASE_next_major/HEAD

Additional context