pdm: sort extras before making the key

...otherwise we seem to get them in the order they are
declared in in pyproject.toml, which seemingly might not
be the same as in the lock file where they are sorted

modules/dream2nix/WIP-python-pdm/lib.nix

@@ -196,7 +196,7 @@
   mkExtrasKey = dep @ {extras ? [], ...}:
     if extras == []
     then "default"
-    else lib.concatStringsSep "," extras;
+    else lib.concatStringsSep "," (lib.naturalSort extras);
 
   # Constructs dependency entry for internal use.
   # We could use the pyproject.nix representation directly instead, but it seems