Fix undefined variable $packagePath in mix:watch error (#485)

When the package is not present in package.json, the correct error is not thrown because $packagePath not exists.

Co-authored-by: Luke Towers <[email protected]>

Author: marcomessa

modules/system/console/MixWatch.php

@@ -45,7 +45,7 @@ public function handle(): int
         $relativeMixJsPath = $package['mix'];
         if (!$this->canCompilePackage($relativeMixJsPath)) {
             $this->error(
-                sprintf('Unable to watch "%s", %s was not found in the package.json\'s workspaces.packages property. Try running mix:install first.', $name, $packagePath)
+                sprintf('Unable to watch "%s", %s was not found in the package.json\'s workspaces.packages property. Try running mix:install first.', $name, $relativeMixJsPath)
             );
             return 1;
         }