Use the PEP 639 SPDX license form so builds work on setuptools 77+

Author: Nathaniel Henry

pyproject.toml

@@ -1,5 +1,5 @@
 [build-system]
-requires = ["setuptools>=68"]
+requires = ["setuptools>=77"]
 build-backend = "setuptools.build_meta"
 
 [project]
@@ -8,15 +8,14 @@ version = "1.0.0"
 description = "Python client for the Close API (api.close.city) — travel times to points of interest for every US census block."
 readme = "README.md"
 requires-python = ">=3.9"
-license = { text = "MIT" }
+license = "MIT"
 license-files = ["LICENSE"]
 authors = [{ name = "Close" }]
 keywords = ["close", "travel-time", "isochrone", "census", "accessibility", "gis"]
 classifiers = [
     "Development Status :: 5 - Production/Stable",
     "Intended Audience :: Science/Research",
     "Intended Audience :: Developers",
-    "License :: OSI Approved :: MIT License",
     "Programming Language :: Python :: 3",
     "Topic :: Scientific/Engineering :: GIS",
 ]