DEV: Rerun AddIndexToPostStatComposerColumns migration (#31765)

The previous version of the migration is not idempotent and can result
in indexes created but marked as "invalid" by Postgres.

Per postgres documentation:

If a problem arises while scanning the table, such as a deadlock or a
uniqueness violation in a unique index,
the CREATE INDEX command will fail but leave behind an "invalid" index.
This index will be ignored for querying
purposes because it might be incomplete; however it will still consume
update overhead. The recommended recovery
  method in such cases is to drop the index and try again to perform
  CREATE INDEX CONCURRENTLY.

db/migrate/20250304041850_add_index_to_post_stat_composer_columns.rb

@@ -1,19 +0,0 @@
-# frozen_string_literal: true
-
-class AddIndexToPostStatComposerColumns < ActiveRecord::Migration[7.2]
-  disable_ddl_transaction!
-
-  def up
-    if !index_exists?(:post_stats, :composer_version)
-      add_index :post_stats, :composer_version, algorithm: :concurrently
-    end
-    if !index_exists?(:post_stats, :writing_device)
-      add_index :post_stats, :writing_device, algorithm: :concurrently
-    end
-  end
-
-  def down
-    remove_index :post_stats, :composer_version if index_exists?(:post_stats, :composer_version)
-    remove_index :post_stats, :writing_device if index_exists?(:post_stats, :writing_device)
-  end
-end

db/migrate/20250311041851_add_index_to_post_stat_composer_columns.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class AddIndexToPostStatComposerColumns < ActiveRecord::Migration[7.2]
+  disable_ddl_transaction!
+
+  def up
+    remove_index :post_stats, :composer_version, algorithm: :concurrently, if_exists: true
+    remove_index :post_stats, :writing_device, algorithm: :concurrently, if_exists: true
+    add_index :post_stats, :composer_version, algorithm: :concurrently
+    add_index :post_stats, :writing_device, algorithm: :concurrently
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end