get rid of PHP warnings

Our error logs are littered with warnings from /advanced-gutenberg/incl/advanced-gutenberg-main.php with php8.2 and WP 6.5.2

The following changes will fix them:

Requires php 7.0

Change line 1033 to:

$block['category'] = sanitize_text_field( $block['category'] ?? '' );

Change line 3413 to:

$current_user_role = $current_user->roles[0] ?? ''; // string

Change line 3437 to:

foreach ( ( $current_user_role ?? [] ) as $cur_ ) {

Change line 4768 to:

if ( $saved_settings['gallery_lightbox'] ?? false ) {