CI builds: installation fails with "error: can't create or remove files in install directory"

[pont-us]

For instance, in https://ci.appveyor.com/project/bcdev/nc2zarr/build/job/fnt7mh20g06u2t5j :

micromamba activate nc2zarr
python setup.py install
running install
error: can't create or remove files in install directory
The following error occurred while trying to add or remove files in the
installation directory:
    [Errno 13] Permission denied: '/usr/local/lib/python2.7/dist-packages/test-easy-install-7573.write-test'
The installation directory you specified (via --install-dir, --prefix, or
the distutils default setting) was:
    /usr/local/lib/python2.7/dist-packages/
Perhaps your account does not have write access to this directory?  If the
installation directory is a system-owned directory, you may need to sign in
as the administrator or "root" account.  If you do not have administrative
access to this machine, you may wish to choose a different installation
directory, preferably one that is listed in your PYTHONPATH environment
variable.
For information on other options, you may wish to consult the
documentation at:
  https://setuptools.readthedocs.io/en/latest/easy_install.html
Please make the appropriate changes for your system and try again.

Given the reference to Python 2.7, this may be due to a change in the default Python version.

[pont-us]

On further investigation, I suspect that this is due to a regression in micromamba: https://github.com/mamba-org/mamba/issues/1288