Fix environment

[ekatef]

Release a restriction of xarray version introduced in #901. A problem which lead previously to troubles, has been fixed in xarray in meantime, and a restricting of xarray version seems to lead to troubles itself: like reported in this PR by @yerbol-akhmetov and by @ Yanonami in a recent Error solve_network in pypsa-eur post in Support channel on Discord.

Changes proposed in this Pull Request

A restriction on xarray version has been removed in this PR. Has tested locally the suggested environment changes, and they seem to work fine.

Checklist

• [x] I consent to the release of this PR's code under the AGPLv3 license and non-code contributions under CC0-1.0 and CC-BY-4.0.
• [x] I tested my contribution locally and it seems to work fine.
• [ ] Code and workflow changes are sufficiently documented.
• [ ] Newly introduced dependencies are added to envs/environment.yaml and doc/requirements.txt.
• [ ] Changes in configuration options are added in all of config.default.yaml and config.tutorial.yaml.
• [ ] Add a test config or line additions to test/ (note tests are changing the config.tutorial.yaml)
• [ ] Changes in configuration options are also documented in doc/configtables/*.csv and line references are adjusted in doc/configuration.rst and doc/tutorial.rst.
• [ ] A note for the release notes doc/release_notes.rst is amended in the format of previous release notes, including reference to the requested PR.

[davide-f]

CI works :D thanks great catch! :) Merged