Remove python 3.8 support

In this cycle, oslo library are dropping the
python3.8 support. Without oslo libs, Tempest
cannot support the python 3.8. Tempest can be run
in virtual env and upstream CI also test the stable
supported branches in virtual env. If anyone want to
test the cloud on python 3.8, they can still run the
Tempest in virtual env python 3.9.

This patch removes the support of python 3.8 and its testing.

Change-Id: I3f540da045c5e89a3f09ce2cf94877c1560f3436

releasenotes/notes/drop-python38-support-c0a696af00110602.yaml

@@ -0,0 +1,8 @@
+---
+prelude: >
+    Tempest dropped the Python 3.8 support.
+upgrade:
+  - |
+    Python 3.8 support has been dropped. Last release of Tempest
+    to support python 3.8 is Temepst 41.0.0. The minimum version
+    of Python now supported by Tempest is Python 3.9.

setup.cfg

@@ -14,7 +14,6 @@ classifier =
     Operating System :: POSIX :: Linux
     Programming Language :: Python
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11

zuul.d/project.yaml

@@ -8,7 +8,6 @@
     check:
       jobs:
         - openstack-tox-pep8
-        - openstack-tox-py38
         - openstack-tox-py39
         - openstack-tox-py310
         - openstack-tox-py311
@@ -127,7 +126,6 @@
     gate:
       jobs:
         - openstack-tox-pep8
-        - openstack-tox-py38
         - openstack-tox-py39
         - openstack-tox-py310
         - openstack-tox-py311