[Nix] typo in tests directory name

flake.nix

@@ -26,7 +26,9 @@
             "Makefile"
             (nix-filter.lib.inDirectory "src")
             (nix-filter.lib.inDirectory "lib")
-            (nix-filter.lib.inDirectory "test")
+            (nix-filter.lib.inDirectory "tests")
+            (nix-filter.lib.inDirectory "config")
+            (nix-filter.lib.inDirectory "stdlib")
             (nix-filter.lib.inDirectory "doc")
           ];
         };
@@ -49,6 +51,7 @@
               pkgs.protobuf
               # For documentation
               pkgs.sphinxHook
+              pkgs.which
             ];
             sphinxBuilders = [
               "html"