Use Python 3.9 as lowest suupported version

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

setup.cfg

@@ -31,6 +31,8 @@ license_files =
     README.rst
 
 [options]
+python_requires = >=3.9
+
 package_dir =
     =src
 packages = find:
@@ -39,7 +41,6 @@ zip_safe = false
 
 setup_requires = setuptools_scm[toml] >= 4
 
-python_requires = >=3.8
 
 install_requires =