Fix incorrect load_dotenv() usage in Django deployment guide (mdn#43114)

* Fix incorrect load_dotenv() usage in Django deployment guide

* Apply suggestion from @hamishwillee

---------

Co-authored-by: Hamish Willee <hamishwillee@gmail.com>

Author: Sarah4908

files/en-us/learn_web_development/extensions/server-side/django/deployment/index.md

@@ -127,8 +127,10 @@ Then open **/locallibrary/settings.py** and insert the following code after `BAS
 # Support env variables from .env file if defined
 import os
 from dotenv import load_dotenv
-env_path = load_dotenv(os.path.join(BASE_DIR, '.env'))
-load_dotenv(env_path)
+
+env_path = os.path.join(BASE_DIR, ".env")
+if os.path.exists(env_path):
+    load_dotenv(env_path)
 ```
 
 This loads the `.env` file from the root of the web application.