revision id is one number behind – publish_post

See this-

function check_values( $post_ID, $post ) {
    $revisions = wp_get_post_revisions( $post_ID );
    $revision_ids = [];
    foreach ( $revisions as $revision ) {
        $revision_ids[] = $revision->ID;
    }
    // $revision_ids; // holds all revision ids
    // $revision_ids[0]; // latest revision
    // $revision_ids[1]; //revision just before the latest one
}

add_action( 'publish_post', 'check_values', 10, 2 );