chore: drop python 3.6 for cibuildwheel driver

This drops python 3.6 for cibuildwheel.
Building python 3.6 packages is still supported.

setup.cfg

@@ -16,7 +16,6 @@ classifiers =
     Natural Language :: English
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3 :: Only
-    Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
@@ -37,10 +36,9 @@ install_requires =
     filelock
     packaging>=20.9
     platformdirs
-    dataclasses;python_version < '3.7'
     tomli;python_version < '3.11'
     typing-extensions>=3.10.0.0;python_version < '3.8'
-python_requires = >=3.6
+python_requires = >=3.7
 include_package_data = True
 zip_safe = False