devShells: make all shells inherit from default shell

Currently, important tools from the default shell are lost as soon as select-shell is used to switch to another shell. select-shell itself, for example is missing, which makes it impossible to switch back to another shell.

lib/inventory/flake-module.nix

@@ -13,6 +13,7 @@ in
       lib,
       config,
       system,
+      self',
       ...
     }:
     let
@@ -26,6 +27,7 @@ in
         inputsFrom = with config.checks; [
           lib-inventory-schema
           lib-inventory-eval
+          self'.devShells.default
         ];
       };