Update pyproject.toml to be PEP639 compliant (#1429)

Author: Kludex

pyproject.toml

@@ -18,6 +18,7 @@ authors = [
     { name = "Alex Hall", email = "[email protected]" },
 ]
 license = "MIT"
+license-files = ["LICENSE"]
 readme = "README.md"
 classifiers = [
     "Development Status :: 5 - Production/Stable",
@@ -32,7 +33,6 @@ classifiers = [
     "Intended Audience :: Developers",
     "Intended Audience :: Information Technology",
     "Intended Audience :: System Administrators",
-    "License :: OSI Approved :: MIT License",
     "Operating System :: Unix",
     "Operating System :: POSIX :: Linux",
     "Environment :: Console",