Raise the baseline to Python 3.9

This is what is supported in CentOS Stream 9 as the system Python,
which makes it meaningful as our new lower bound for supported Python
versions.

Signed-off-by: Neal Gompa <neal@gompa.dev>

dev/containers/tox_py3.sh

@@ -23,4 +23,4 @@ git --no-pager log -2
 fi
 
 export LANG="en_US.UTF-8"
-tox -v -e "${PYVER:-py38}" -- ${TESTCASE:-tests/}
+tox -v -e "${PYVER:-py39}" -- ${TESTCASE:-tests/}

setup.py

@@ -69,12 +69,10 @@ setup(
         "License :: OSI Approved :: GNU General Public License v2 or later (GPLv2+)",
         "Operating System :: POSIX :: Linux",
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.4",
-        "Programming Language :: Python :: 3.5",
-        "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",
         "Topic :: Internet :: WWW/HTTP :: WSGI :: Application",
         "Topic :: Software Development :: Bug Tracking",
         "Topic :: Software Development :: Version Control",

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py{37,38,39}
+envlist = py{39,310,311,312}
 skipsdist = True
 # If the user is missing an interpreter, don't fail
 skip_missing_interpreters = True