Gets the URL to learn more about updating the PHP version the site is running on.

This URL can be overridden by specifying an environment variable `WP_UPDATE_PHP_URL` or by using the
{@see ‘wp_update_php_url’} filter. Providing an empty string is not allowed and will result in the
default URL being used. Furthermore the page the URL links to should preferably be localized in the
site language.

function wp_get_update_php_url() {
	$default_url = wp_get_default_update_php_url();

	$update_url = $default_url;
	if ( false !== getenv( 'WP_UPDATE_PHP_URL' ) ) {
		$update_url = getenv( 'WP_UPDATE_PHP_URL' );
	}

	/**
	 * Filters the URL to learn more about updating the PHP version the site is running on.
	 *
	 * Providing an empty string is not allowed and will result in the default URL being used. Furthermore
	 * the page the URL links to should preferably be localized in the site language.
	 *
	 * @since 5.1.0
	 *
	 * @param string $update_url URL to learn more about updating PHP.
	 */
	$update_url = apply_filters( 'wp_update_php_url', $update_url );

	if ( empty( $update_url ) ) {
		$update_url = $default_url;
	}

	return $update_url;
}