Switch license metadata to the PEP 639 format

License classifiers and the table form of `license` are now deprecated.

Author: SpecLad

pyproject.toml

@@ -1,5 +1,5 @@
 [build-system]
-requires = ["flit_core >=3.2,<4"]
+requires = ["flit_core >=3.11,<4"]
 build-backend = "flit_core.buildapi"
 
 [project]
@@ -8,11 +8,11 @@ authors = [
     {name = "Thomas Kluyver", email = "thomas@kluyver.me.uk"},
 ]
 readme = "README.rst"
-license = {file = "LICENSE"}
+license = "MIT"
+license-files = ["LICENSE"]
 requires-python = ">=3.8"
 dependencies = []
 classifiers = [
-    "License :: OSI Approved :: MIT License",
     "Programming Language :: Python :: 3",
     "Programming Language :: Python :: 3 :: Only",
 ]