[Security] Improve requires_channel var naming

Author: momito69

security/force_https.rst

@@ -74,8 +74,8 @@ access control:
             };
 
 To make life easier while developing, you can also use an environment variable,
-like ``requires_channel: '%env(SECURE_SCHEME)%'``. In your ``.env`` file, set
-``SECURE_SCHEME`` to ``http`` by default, but override it to ``https`` on production.
+like ``requires_channel: '%env(REQUIRED_SCHEME)%'``. In your ``.env`` file, set
+``REQUIRED_SCHEME`` to ``http`` by default, but override it to ``https`` on production.
 
 See :doc:`/security/access_control` for more details about ``access_control``
 in general.