pyproject.toml: advertise Python 3.12 support

Signed-off-by: Bastian Krause <bst@pengutronix.de>

pyproject.toml

@@ -28,6 +28,7 @@ classifiers = [
     "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
     "License :: OSI Approved :: GNU Lesser General Public License v2 or later (LGPLv2+)",
 ]
 dependencies = [
@@ -216,7 +217,7 @@ signature-mutators = ["labgrid.step.step"]
 [tool.tox]
 legacy_tox_ini = """
 [tox]
-envlist = py38, py39, py310, py311
+envlist = py38, py39, py310, py311, py312
 isolated_build = true
 
 [testenv]