Remove Python 3.8 support

Tempest is now removing Python 3.8 support from master[1]. So drop
the same from this plugin.

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

Change-Id: Ieec4772eaa3701a0b636d7af8d800055314d5c9c

releasenotes/notes/drop-python38-28fd72eff86e858e.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    Python 3.8 support has been dropped. Last release of
+    zaqar-tempest-plugin to support python 3.8 is 2.0.0.
+    The minimum version of Python now supported is Python 3.9.

setup.cfg

@@ -6,7 +6,7 @@ description_file =
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page = http://www.openstack.org/
-python_requires = >=3.8
+python_requires = >=3.9
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -17,7 +17,6 @@ classifier =
     Programming Language :: Python :: Implementation :: CPython
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11