fix: Upsize LTI Discussions iframe, 400px -> 800px

Otherwise, there's too much scrolling.

Fixes: https://openedx.atlassian.net/browse/TNL-7996

openedx/features/lti_course_tab/tab.py

@@ -143,7 +143,7 @@ class LtiCourseLaunchMixin:
             """
             #lti-tab-embed {
                 width: 100%;
-                min-height: 400px;
+                min-height: 800px;
                 border: none;
             }
             """