Connectors: Remove unnecessary null coalescing for authentication method.

The `method` key is always present in the defaults array, so the
`?? ''` fallback is not needed.

See #64957.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: gziolo

src/wp-includes/connectors.php

@@ -343,7 +343,7 @@ function _wp_connectors_register_default_ai_providers( WP_Connector_Registry $re
 
 	// Register all default connectors directly on the registry.
 	foreach ( $defaults as $id => $args ) {
-		if ( 'api_key' === ( $args['authentication']['method'] ?? '' ) ) {
+		if ( 'api_key' === $args['authentication']['method'] ) {
 			$sanitized_id = str_replace( '-', '_', $id );
 
 			if ( ! isset( $args['authentication']['setting_name'] ) ) {