Fixes the compatibility of XML-RPC library with PHP 8 - Orig PR6264

[NielBuys]

Merging pull request: bcit-ci#6264

[NielBuys]

Fixed warnings bcit-ci#6306

[jamieburchell]

@NielBuys Heads up, the tests don't appear to run on PHPUnit 10+:

$ composer run test:coverage
> @putenv XDEBUG_MODE=coverage
> phpunit --color=always --coverage-text --configuration tests/phpunit.xml
PHP Fatal error:  Cannot override final method PHPUnit\Framework\TestCase::runBare() in /home/jamie/projects/CodeIgniter/tests/mocks/ci_testcase.php on line 349

Fatal error: Cannot override final method PHPUnit\Framework\TestCase::runBare() in /home/jamie/projects/CodeIgniter/tests/mocks/ci_testcase.php on line 349
Script phpunit --color=always --coverage-text --configuration tests/phpunit.xml handling the test:coverage event returned with error code 255

[NielBuys]

@jamieburchell Thanks I will look into it.