Use a text field for license in pyproject.toml (#442)

When using the "file" field type, PyPI putting the entire contents of
the file into the license field and mislabeling it as MIT. Replace it
with just the string for the license name and not the contents of the
file.

pyproject.toml

@@ -1,26 +1,22 @@
-[build-system]
-requires = ["setuptools>=61", "wheel", "setuptools_scm[toml]>=8.0.3"]
-build-backend = "setuptools.build_meta"
-
 [project]
 name = "harmonica"
 description = "Forward modeling, inversion, and processing gravity and magnetic data"
 dynamic = ["version"]
 authors = [
- { name="The Harmonica Developers", email="[email protected]" },
+ {name="The Harmonica Developers", email="[email protected]"},
 ]
 maintainers = [
  {name = "Santiago Soler", email = "[email protected]"}
 ]
 readme = "README.md"
-requires-python = ">=3.8"
-license = {file = "LICENSE.txt"}
+license = {text = "BSD-3-Clause"}
 keywords = ["geoscience", "geophysics"]
 classifiers = [
  "Programming Language :: Python :: 3",
- "License :: OSI Approved :: MIT License",
+ "License :: OSI Approved :: BSD License",
  "Operating System :: OS Independent",
 ]
+requires-python = ">=3.8"
 dependencies = [
  "numpy >= 1.21",
  "pandas >= 1.1",
@@ -46,6 +42,10 @@ dependencies = [
 visualizations = ["pyvista>=0.27", "vtk>=9"]
 numba_progress = ["numba_progress"]
 
+[build-system]
+requires = ["setuptools>=61", "wheel", "setuptools_scm[toml]>=8.0.3"]
+build-backend = "setuptools.build_meta"
+
 [tool.setuptools_scm]
 version_scheme = "post-release"
 local_scheme = "node-and-date"