Fix #278: Follow PEP 639: use SPDX-expression for license

* PEP 639: use SPDX-expression for license
* remove license classifier
* require setuptools >= 77, see pypa/setuptools#4706

Author: prauscher

pyproject.toml

@@ -1,13 +1,13 @@
 [build-system]
 build-backend = "setuptools.build_meta"
-requires = [ "setuptools>=61.2" ]
+requires = [ "setuptools>=77" ]
 
 [project]
 name = "django-csp"
 version = "4.0"
 description = "Django Content Security Policy support."
 readme = "README.rst"
-license = { text = "BSD" }
+license = "BSD-3-Clause"
 maintainers = [
   { name = "Mozilla MEAO team", email = "[email protected]" },
 ]
@@ -21,7 +21,6 @@ classifiers = [
   "Framework :: Django :: 5.1",
   "Framework :: Django :: 5.2",
   "Intended Audience :: Developers",
-  "License :: OSI Approved :: BSD License",
   "Operating System :: OS Independent",
   "Programming Language :: Python",
   "Programming Language :: Python :: 3 :: Only",