fix: Fix bug causing build_user_filter to filter incorrectly. (#1072)

student_id in Submissions refers to the Course Reg ID, not the User ID.

Author: GabrielCWT

lib/cadet/assessments/assessments.ex

@@ -1505,7 +1505,9 @@ defmodule Cadet.Assessments do
             submission.student_id in subquery(
               from(user in User,
                 where: ilike(user.name, ^"%#{value}%"),
-                select: user.id
+                inner_join: cr in CourseRegistration,
+                on: user.id == cr.user_id,
+                select: cr.id
               )
             )
         )
@@ -1517,7 +1519,9 @@ defmodule Cadet.Assessments do
             submission.student_id in subquery(
               from(user in User,
                 where: ilike(user.username, ^"%#{value}%"),
-                select: user.id
+                inner_join: cr in CourseRegistration,
+                on: user.id == cr.user_id,
+                select: cr.id
               )
             )
         )