Inplace update fails with Implicit naming of numpy indexers

[ricardoV94]

What happened?

import xarray as xr

x = xr.DataArray(np.zeros((2, 3)), dims=("a", "b"))
assert x[("b", np.array([0, 1, 0])),].shape == (3,)

x[("b", np.array([0, 1, 0])),] += 1  # ValueError: setting an array element with a sequence. The requested array has an inhomogeneous shape after 1 dimensions. The detected shape was (2,) + inhomogeneous part.

Under the hood, this ends up being called, which fails:

x.variable[("b", np.array([0, 1, 0])),]

[welcome]

Thanks for opening your first issue here at xarray! Be sure to follow the issue template!
If you have an idea for a solution, we would really welcome a Pull Request with proposed changes.
See the Contributing Guide for more.
It may take us a while to respond here, but we really value your contribution. Contributors like you help make xarray better.
Thank you!