pyproject.toml: Update metadata

Author: mkoeppe

pyproject.toml

@@ -17,18 +17,18 @@ authors = [
 ]
 dependencies = []
 requires-python = ">=3.9"
-license = {text = "GPLv2+"}
+license = "GPL-2.0-or-later"
 keywords = ["integer programming", "cutting planes"]
 classifiers = [
     "Development Status :: 5 - Production/Stable",
     "Intended Audience :: Science/Research",
-    "License :: OSI Approved :: GNU General Public License v2 or later (GPLv2+)",
     "Programming Language :: Python",
     "Programming Language :: Python :: 3",
     "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
     "Topic :: Scientific/Engineering :: Mathematics",
 ]
 dynamic = ['version']