Fix devel test python version (#593)

Author: Qalthos

.github/workflows/tox.yml

@@ -35,7 +35,7 @@ jobs:
     with:
       run_pre: ./tools/test-setup.sh
       max_python: "3.13"
-      default_python: "3.11" # min version, for 'lint' in particular
+      default_python: "3.12" # min version of `devel`
       jobs_producing_coverage: 9
       other_names_also: |
         devspaces