Declare license via (the accepted) PEP 639.

The License field is deprecated, as is the trove classifier.

Note that pip show does not support properly detecting these yet,
but it will.

Note also that `pip-licenses` does not support PEP 639 (see
raimon49/pip-licenses#213) the implications of which are that we are
already broken (the `license_check` noxenv fails because of packages
already using the newer standard). This doesn't fix that yet. AFAICT no
tool exists that does this properly yet/now. So let's see... I guess we
reimplement that functionality?!

Refs: https://peps.python.org/pep-0639/
Refs: pypa/pip#13112
Refs: pypa/pip#6677

jsonschema/tests/test_cli.py

@@ -881,11 +881,8 @@ def test_useless_error_format(self):
 
 class TestCLIIntegration(TestCase):
     def test_license(self):
-        output = subprocess.check_output(
-            [sys.executable, "-m", "pip", "show", "jsonschema"],
-            stderr=subprocess.STDOUT,
-        )
-        self.assertIn(b"License: MIT", output)
+        our_metadata = metadata.metadata("jsonschema")
+        self.assertEqual(our_metadata.get("License-Expression"), "MIT")
 
     def test_version(self):
         version = subprocess.check_output(

pyproject.toml

@@ -9,7 +9,8 @@ source = "vcs"
 name = "jsonschema"
 description = "An implementation of JSON Schema validation for Python"
 requires-python = ">=3.9"
-license = {text = "MIT"}
+license = "MIT"
+license-files = ["COPYING"]
 keywords = [
     "validation",
     "data validation",
@@ -23,7 +24,6 @@ authors = [
 classifiers = [
   "Development Status :: 5 - Production/Stable",
   "Intended Audience :: Developers",
-  "License :: OSI Approved :: MIT License",
   "Operating System :: OS Independent",
   "Programming Language :: Python",
   "Programming Language :: Python :: 3.9",