enqueue script with get_shortcode_regex

There’s already a function for checking if a post has a shortcode: has_shortcode():

function enqueue_script_if_shortcode_is_detected() {
    global $post;

    wp_register_script( 'leweb-widgets', get_stylesheet_directory_uri() . '/includes/leweb-widgets.php', '1.0', true );

    if ( has_shortcode( $post->post_content, 'leweb_suggested_events' ) ) {
        wp_enqueue_script('leweb-widgets');
    }
}
add_action( 'wp_enqueue_scripts', 'enqueue_script_if_shortcode_is_detected' );

Just keep in mind that checking the post this way:

1. Will not know if the shortcode is used in a widget or custom field.
2. Will not work properly on archive pages.
3. Is using the global $post variable, which should be avoided where possible. Especially outside the loop.

I’d advise checking is_singular() and using get_queried_object() to get the current post.

function enqueue_script_if_shortcode_is_detected() {
    wp_register_script( 'leweb-widgets', get_stylesheet_directory_uri() . '/includes/leweb-widgets.php', '1.0', true );

    if ( is_singular() ) {
        $post = get_queried_object();

        if ( has_shortcode( $post->post_content, 'leweb_suggested_events' ) ) {
            wp_enqueue_script('leweb-widgets');
        }
    }
}
add_action( 'wp_enqueue_scripts', 'enqueue_script_if_shortcode_is_detected' );

But if your script is loaded in the footer, which yours is, you’ll get more reliable results if you add wp_enqueue_script('leweb-widgets'); to the shortcode callback. This way you can be sure the script will be loaded whenever the shortcode is used, no matter where it’s used.