Remove support for Python 3.9

Support for Python 3.9 has been removed. Now Python 3.10 is the minimum
version supported.

Change-Id: If1066d05e905ef4c639278d0457177875e97871d
Signed-off-by: Riccardo Pittau <elfosardo@gmail.com>

releasenotes/notes/remove-py39-fca5d9e7d2e135cf.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    Support for Python 3.9 has been removed. Now Python 3.10 is the minimum
+    version supported.

setup.cfg

@@ -7,7 +7,7 @@ author_email = openstack-discuss@lists.openstack.org
 home_page = https://docs.openstack.org/ironic-python-agent/
 summary = Ironic Python Agent Ramdisk
 license = Apache-2
-python_requires = >=3.9
+python_requires = >=3.10
 classifier =
     Environment :: OpenStack
     Intended Audience :: System Administrators
@@ -18,7 +18,6 @@ classifier =
     Programming Language :: Python :: Implementation :: CPython
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11
     Programming Language :: Python :: 3.12