build: Bump minimum Python version to v3.9

Author: seifertm

setup.cfg

@@ -21,7 +21,6 @@ classifiers =
 
   License :: OSI Approved :: Apache Software License
 
-  Programming Language :: Python :: 3.8
   Programming Language :: Python :: 3.9
   Programming Language :: Python :: 3.10
   Programming Language :: Python :: 3.11
@@ -35,7 +34,7 @@ classifiers =
   Typing :: Typed
 
 [options]
-python_requires = >=3.8
+python_requires = >=3.9
 packages = pytest_asyncio
 include_package_data = True