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.

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

Author: Julian

pyproject.toml

@@ -10,14 +10,15 @@ name = "referencing"
 description = "JSON Referencing + Python"
 requires-python = ">=3.9"
 readme = "README.rst"
+license = "MIT"
+license-files = ["COPYING"]
 keywords = ["json", "referencing", "jsonschema", "openapi", "asyncapi"]
 authors = [
   { name = "Julian Berman", email = "Julian+referencing@GrayVines.com" },
 ]
 classifiers = [
   "Development Status :: 3 - Alpha",
   "Intended Audience :: Developers",
-  "License :: OSI Approved :: MIT License",
   "Operating System :: OS Independent",
   "Programming Language :: Python",
   "Programming Language :: Python :: 3.9",
@@ -65,8 +66,8 @@ skip_covered = true
 
 [tool.doc8]
 ignore = [
-    "D000",  # see PyCQA/doc8#125
-    "D001",  # one sentence per line, so max length doesn't make sense
+  "D000",  # see PyCQA/doc8#125
+  "D001",  # one sentence per line, so max length doesn't make sense
 ]
 
 [tool.mypy]
@@ -77,8 +78,8 @@ ignore_errors = true
 reportUnnecessaryTypeIgnoreComment = true
 strict = ["**/*"]
 exclude = [
-    "**/tests/__init__.py",
-    "**/tests/test_*.py",
+  "**/tests/__init__.py",
+  "**/tests/test_*.py",
 ]
 
 [tool.ruff]