Update link for KZ test cutouts

Changes proposed in this Pull Request

Good day. Here I propose to update the outdated link to the test cutouts for KZ which is used in CI/CD of pypsa-kz-data repository.

[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.