PHP 8.1 deprecation notices in demo/plugins/cacheresource.pdo.php

[alexgit2k]

With PHP 8.1 there are several deprecation notices in demo/plugins/cacheresource.pdo.php:

line 247: Optional parameter $cache_id declared before required parameter $content is implicitly treated as a required parameter
line 199: Optional parameter $cache_id declared before required parameter $mtime is implicitly treated as a required parameter
line 247: Optional parameter $compile_id declared before required parameter $content is implicitly treated as a required parameter
line 199: Optional parameter $compile_id declared before required parameter $mtime is implicitly treated as a required parameter

[marclaporte]

Related: #678