Access schema migration object via base connection in Heroku task

Because: This behaviour was removed in rails 7.1.

See https://github.com/rails/rails/blob/7-1-stable/activerecord/CHANGELOG.md#:~:text=Move%20ActiveRecord%3A%3ASchemaMigration%20to%20an%20independent%20object

lib/tasks/heroku.rake

@@ -1,7 +1,7 @@
 namespace :heroku do
   desc 'Heroku release task - runs on every code push, runs before postdeploy task'
   task release: :environment do
-    if ActiveRecord::SchemaMigration.table_exists?
+    if ActiveRecord::Base.connection.schema_migration.table_exists?
       Rake::Task['db:migrate'].invoke
       Rake::Task['db:seed'].invoke
       Rake::Task['curriculum:content:import'].invoke