fix: enabling the notes tool using the course authoring will now add the notes tab (#29093)

If an existing course doesn't already have the notes tab, enabling notes will not make it show up. This change fixes this by adding the tab in case it isn't already in the course.

lms/djangoapps/edxnotes/plugins.py

@@ -13,6 +13,7 @@ from lms.djangoapps.courseware.tabs import EnrolledTab
 from openedx.core.djangoapps.content.course_overviews.models import CourseOverview
 from openedx.core.djangoapps.course_apps.plugins import CourseApp
 from openedx.core.lib.courses import get_course_by_id
+from xmodule.tabs import CourseTab, CourseTabList
 
 User = get_user_model()
 
@@ -79,6 +80,12 @@ class EdxNotesCourseApp(CourseApp):
         """
         course = get_course_by_id(course_key)
         course.edxnotes = enabled
+        if enabled:
+            notes_tab = CourseTabList.get_tab_by_id(course.tabs, 'edxnotes')
+            if notes_tab is None:
+                # If the course doesn't already have the notes tab, add it.
+                notes_tab = CourseTab.load("edxnotes")
+                course.tabs.append(notes_tab)
         modulestore().update_item(course, user.id)
         return enabled