Remove support for Python 3.8

Change-Id: Ic62e880d2bc5fd8ef7ee7f13675a9742eccc697a
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

releasenotes/notes/remove-py38-3c686984d115bccd.yaml

@@ -0,0 +1,4 @@
+---
+upgrade:
+  - |
+    Python 3.8 is no longer supported.

setup.cfg

@@ -6,7 +6,7 @@ summary = Config files from cloud metadata
 description_file =
     README.rst
 home_page = https://opendev.org/openstack/os-apply-config
-python_requires = >=3.8
+python_requires = >=3.9
 classifier =
     Development Status :: 4 - Beta
     Environment :: Console
@@ -18,7 +18,6 @@ classifier =
     Programming Language :: Python
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3 :: Only
-    Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11