Remove trailing slash from SITE_URL (#9559) (#9560)

- ref: https://github.com/inventree/InvenTree/discussions/9552
- ref: https://stackoverflow.com/questions/56404930/when-trying-set-corsheaders-in-settings-py-file

(cherry picked from commit 527652007e934bc05476859ab3ec4fbdffb313db)

Co-authored-by: Oliver <oliver.henry.walters@gmail.com>

src/backend/InvenTree/InvenTree/settings.py

@@ -1095,6 +1095,7 @@ IMPORT_EXPORT_USE_TRANSACTIONS = True
 SITE_URL = get_setting('INVENTREE_SITE_URL', 'site_url', None)
 
 if SITE_URL:
+    SITE_URL = str(SITE_URL).strip().rstrip('/')
     logger.info('Using Site URL: %s', SITE_URL)
 
     # Check that the site URL is valid