fix: add missing platformdirs dependency to cookiecutter templates PEP 723 syntax

Author: 56kyle

noxfile.py

@@ -1,7 +1,7 @@
 """Noxfile for the cookiecutter-robust-python template."""
 
 # /// script
-# dependencies = ["nox>=2025.5.1", "python-dotenv>=1.0.0"]
+# dependencies = ["nox>=2025.5.1", "platformdirs>=4.3.8", "python-dotenv>=1.0.0"]
 # ///
 
 import os