tests: stub neovim and vimPlugins and darwin (#6779)

Author: khaneliman

tests/default.nix

@@ -141,6 +141,7 @@ let
       "ne"
       "neomutt"
       "neovide"
+      "neovim"
       "nheko"
       "nix"
       "nix-index"
@@ -185,6 +186,7 @@ let
       "translate-shell"
       "vifm"
       "vim-vint"
+      "vimPlugins"
       "vscode"
       "watson"
       "wezterm"