Set version to v0.3.1, update for python 3.12 (#62)

Author: adrianeboyd

setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = weasel
-version = 0.3.0
+version = 0.3.1
 description = Weasel: A small and easy workflow system
 url = https://github.com/explosion/weasel/
 author = Explosion
@@ -23,6 +23,7 @@ classifiers =
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11
+    Programming Language :: Python :: 3.12
     Topic :: Scientific/Engineering
 project_urls =
     Release notes = https://github.com/explosion/weasel/releases