Adjust vaccination source backfilling logic

This is a small change to the migration which adds source as a column to the VaccinationRecord table.

For historically uploaded vaccination records with the outcome `already_had` created before the migration, we now backfill the source value as `historical_upload` rather than `consent_refusal`. This is consistent with how those records are treated after the migration.

Jira-Issue: MAV-1603

Author: samcoy3

db/migrate/20250829172505_add_source_to_vaccination_record.rb

@@ -4,11 +4,12 @@ class AddSourceToVaccinationRecord < ActiveRecord::Migration[8.0]
   def up
     add_column :vaccination_records, :source, :integer
 
-    # Backfill values based on presence of session_id
     VaccinationRecord.update_all(source: "historical_upload")
-    VaccinationRecord.where(outcome: "already_had").update_all(
-      source: "consent_refusal"
-    )
+    # This handles records which were created when a parent refused consent because the patient was already vaccinated
+    VaccinationRecord.where(
+      outcome: "already_had",
+      immunisation_imports: []
+    ).update_all(source: "consent_refusal")
     VaccinationRecord.recorded_in_service.update_all(source: "service")
 
     change_column_null :vaccination_records, :source, false