Remove support for Pyton 3.8 and older

Python 3.6 and 3.7 are not supported any of active stable branches now,
so no longer need to be supported.

Also remove Python 3.8 support according to [1].

[1]
https://lists.openstack.org/archives/list/openstack-discuss@lists.openstack.org/thread/FOWV4UQZTH4DPDA67QDEROAESYU5Z3LE/

Also add a few new versions currently tested.

Change-Id: I9d2fb3476f9fbbc7ae4e3c787e4dc7d69b93e6bf
diff --git a/releasenotes/notes/drop-python38-support-c5d27b136d2222b9.yaml b/releasenotes/notes/drop-python38-support-c5d27b136d2222b9.yaml
new file mode 100644
index 0000000..511fb7b
--- /dev/null
+++ b/releasenotes/notes/drop-python38-support-c5d27b136d2222b9.yaml
@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    Support for Python 3.8 has been dropped. Latest release of
+    octavia-tempest-plugin to support python 3.8 is 2.8.0.
+    The minimum version of Python now supported is Python 3.9.
diff --git a/setup.cfg b/setup.cfg
index cb30ba5..45e5030 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -6,7 +6,7 @@
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page = https://docs.openstack.org/octavia-tempest-plugin/latest/
-python_requires = >=3.6
+python_requires = >=3.9
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -17,9 +17,10 @@
     Programming Language :: Python :: Implementation :: CPython
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.6
-    Programming Language :: Python :: 3.7
-    Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
+    Programming Language :: Python :: 3.10
+    Programming Language :: Python :: 3.11
+    Programming Language :: Python :: 3.12
 
 [files]
 packages =