Adapt license declaration in pyproject.toml to new PEP 639.
This fixes ERROR InvalidDistribution: Invalid distribution metadata: unrecognized or malformed field 'license-file'
when building the package as in https://git.gfz-potsdam.de/EnMAP/sicor/-/jobs/267143.
Signed-off-by: Daniel Scheffler danschef@gfz.de
Edited by Daniel Scheffler