[release] compatibility fixes for matplotlib 3.9

See merge request !44

add tests for mpl 3.9

See merge request !43

as a colorbar update apparently decreases the size of the axes with mpl 3.9.1.

numpy <2.0.0

[release] Implement validate_legend_loc (#31)

See merge request !42

Update psyplot min version

See merge request !41

update skeleton

See merge request !40

fix image comparison and add reference and test images as CI artifacts

See merge request !39

add mpl ci matrix

See merge request !38

use pytest-xdist in tests

See merge request !37

and run tests on large CI runner, see see https://hifis.net/doc/software/gitlab/ci/#linux-shared-runners

migrate to python-package-template

See merge request !36

as this changed in mpl 3.3

as this method has been deprecated in mpl 3.4

Compatibility fixes

Changed
=======

- We now use the new `convert_coordinate` method that has been introduced with
  psyplot v1.4.1 (see psyplot/psyplot#39 and #30)

Fixed
=====
- psy-simple is now compatible with matplotlib 3.5 (see #31)