FIX: Missing table check in post_migration (#1068)

db/post_migrate/20250114184356_drop_old_embedding_tables2.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 class DropOldEmbeddingTables2 < ActiveRecord::Migration[7.2]
   def up
+    if table_exists?(:ai_document_fragment_embeddings)
       # Copy rag embeddings created during deploy.
       execute <<~SQL
           INSERT INTO ai_document_fragments_embeddings (rag_document_fragment_id, model_id, model_version, strategy_id, strategy_version, digest, embeddings, created_at, updated_at)
@@ -15,6 +16,7 @@ class DropOldEmbeddingTables2 < ActiveRecord::Migration[7.2]
             WHERE target.rag_document_fragment_id IS NULL
           )
         SQL
+    end
 
     execute <<~SQL
         DROP INDEX IF EXISTS ai_topic_embeddings_1_1_search_bit;