Fix --only flag silently dropping custom post type IDs

When --only is used with explicit post IDs, the query still applied the
default post_type constraint (['post', 'page']), so any IDs belonging to
custom post types were dropped from the migration queue without warning.

Set post_type='any' inside the --only branch so all explicitly supplied
IDs are respected regardless of their post type.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: jessedyck

includes/ConvertToBlocks/MigrationAgent.php

@@ -223,7 +223,8 @@ public function get_posts_to_update( $opts = [] ) {
 			$post_in = array_map( 'intval', $post_in );
 			$post_in = array_filter( $post_in );
 
-			$query_params['post__in'] = $post_in;
+			$query_params['post__in']  = $post_in;
+			$query_params['post_type'] = 'any';
 		}
 
 		$query = new \WP_Query( $query_params );