Add an apply StringConversionInInterpolation rule

.rubocop_basic.yml

@@ -126,6 +126,9 @@ Lint/LiteralAsCondition:
 Lint/ShadowingOuterLocalVariable:
   Enabled: true
 
+Lint/StringConversionInInterpolation:
+  Enabled: true
+
 Lint/UselessAssignment:
   Enabled: true
 

app/models/poll/partial_result.rb

@@ -21,9 +21,9 @@ class Poll::PartialResult < ApplicationRecord
 
   def update_logs
     if amount_changed? && amount_was.present?
-      self.amount_log += ":#{amount_was.to_s}"
-      self.officer_assignment_id_log += ":#{officer_assignment_id_was.to_s}"
-      self.author_id_log += ":#{author_id_was.to_s}"
+      self.amount_log += ":#{amount_was}"
+      self.officer_assignment_id_log += ":#{officer_assignment_id_was}"
+      self.author_id_log += ":#{author_id_was}"
     end
   end
 end