Restore use_transactional_tests value after delete

This is needed for specs that have the :delete metadata on a specific
example and not on the whole file / class.

Without this, succeeding tests in the same file would run without any
transaction wrapper and without any DB cleanup.

spec/support/database_cleaner.rb

@@ -52,6 +52,8 @@ RSpec.configure do |config|
     example.run
 
     delete_from_all_tables!(except: deletion_except_tables)
+
+    self.class.use_transactional_tests = true
   end
 
   config.around(:each, :migration) do |example|
@@ -60,5 +62,7 @@ RSpec.configure do |config|
     example.run
 
     delete_from_all_tables!
+
+    self.class.use_transactional_tests = true
   end
 end