refactor: Change variables to follow new format

Author: GabrielCWT

lib/cadet_web/templates/email/assessment_submission.html.eex

@@ -1,5 +1,5 @@
 <p> Dear <%= @avenger_name %>,</p>
 
-<p> There is a new submission by <%= @student_name %> for <a href="<%= @submission_url %>"><%= @assessment_title %></a>. Please Review and grade the submission.</p>
+<p> There is a new submission by <%= @student_name %> for <a href="<%= @submission.submission_url %>"><%= @submission.assessment.title %></a>. Please Review and grade the submission.</p>
 
 <a href="/">Unsubscribe</a> from this email topic.