build: fixup pyproject.toml per newest Hatchling release

[MarcoGorelli]

There's a new release of hatchling is causing the build to fail:

https://github.com/narwhals-dev/narwhals/actions/runs/11764476318/job/32769662368?pr=1326:

Traceback (most recent call last):
  File "<string>", line 11, in <module>
  File "/home/runner/work/_temp/setup-uv-cache/builds-v0/.tmpqjAseZ/lib/python3.12/site-packages/hatchling/build.py", line 83, in build_editable
    return os.path.basename(next(builder.build(directory=wheel_directory, versions=['editable'])))
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/_temp/setup-uv-cache/builds-v0/.tmpqjAseZ/lib/python3.12/site-packages/hatchling/builders/plugin/interface.py", line 90, in build
    self.metadata.validate_fields()
  File "/home/runner/work/_temp/setup-uv-cache/builds-v0/.tmpqjAseZ/lib/python3.12/site-packages/hatchling/metadata/core.py", line 266, in validate_fields
    self.core.validate_fields()
  File "/home/runner/work/_temp/setup-uv-cache/builds-v0/.tmpqjAseZ/lib/python3.12/site-packages/hatchling/metadata/core.py", line 1363, in validate_fields
    getattr(self, attribute)
  File "/home/runner/work/_temp/setup-uv-cache/builds-v0/.tmpqjAseZ/lib/python3.12/site-packages/hatchling/metadata/core.py", line 753, in license_files
    raise TypeError(message)
TypeError: Field `project.license-files` must be an array

This fixes that, but it looks like there's also an issue with hatch run which may need patching in hatchling pypa/hatch#1793

[MarcoGorelli]

hatchling have put out a new release, and this has fixed that, so this can be closed 🥳