Fix warning on nix lazy-trees

`warning: Performing inefficient double copy of path 'X' to the store. This can typically be avoided by rewriting an attribute like `src = ./.` to `src = builtins.path { path = ./.; name = "source"; }`.`

flake.nix

@@ -39,7 +39,10 @@
             format = "pyproject";
             nativeBuildInputs = with python.pkgs; [ poetry-core ];
             propagatedBuildInputs = with python.pkgs; [ requests beautifulsoup4 colorama ];
-            src = ./.;
+            src = builtins.path {
+              name = "hydra-check-source";
+              path = ./.;
+            };
             checkInputs = with python.pkgs; [ mypy ];
             checkPhase = ''
               #export MYPYPATH=$PWD/src