Fix support for PHP 8.4 and above

[TheIndra55]

Makes the following changes:

• Update packages to support PHP 8.4 (mostly Twig)
• Fix a cast that was deprecated in PHP 8.5

We're still using two packages that are both unmaintained and have a deprecation warning, so not sure what to do with those, but it's only a warning and we have some time.

PHP Deprecated:  Yosymfony\Toml\Parser::syntaxError(): Implicitly marking parameter $token as nullable is deprecated, the explicit nullable type must be used instead in C:\Users\Indra\source\repos\DeerLister\vendor\yosymfony\toml\src\Parser.php on line 581
PHP Deprecated:  Parsedown::blockSetextHeader(): Implicitly marking parameter $Block as nullable is deprecated, the explicit nullable type must be used instead in C:\Users\Indra\source\repos\DeerLister\vendor\erusev\parsedown\Parsedown.php on line 715
PHP Deprecated:  Parsedown::blockTable(): Implicitly marking parameter $Block as nullable is deprecated, the explicit nullable type must be used instead in C:\Users\Indra\source\repos\DeerLister\vendor\erusev\parsedown\Parsedown.php on line 853