[2.x] Suppress PHP 8 deprecation notice for Iterator implementation methods

[ElfSundae]

I am using PHP 8.1 and there is a third-party library that depends on php-dot-notation 2.x, my PHP logs have too many these notices 😭
If there are no other issues, Please merge this PR and publish a new version for 2.x, thanks a lot 👍

PHP Deprecated: Return type of Adbar\Dot::offsetExists($key) should either be compatible with ArrayAccess::offsetExists(mixed $offset): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /Users/elfsundae/data/projects/php/aliyun-tea-php/vendor/adbario/php-dot-notation/src/Dot.php on line 510
PHP Deprecated: Return type of Adbar\Dot::offsetGet($key) should either be compatible with ArrayAccess::offsetGet(mixed $offset): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /Users/elfsundae/data/projects/php/aliyun-tea-php/vendor/adbario/php-dot-notation/src/Dot.php on line 521
PHP Deprecated: Return type of Adbar\Dot::offsetSet($key, $value) should either be compatible with ArrayAccess::offsetSet(mixed $offset, mixed $value): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /Users/elfsundae/data/projects/php/aliyun-tea-php/vendor/adbario/php-dot-notation/src/Dot.php on line 532
PHP Deprecated: Return type of Adbar\Dot::offsetUnset($key) should either be compatible with ArrayAccess::offsetUnset(mixed $offset): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /Users/elfsundae/data/projects/php/aliyun-tea-php/vendor/adbario/php-dot-notation/src/Dot.php on line 548

[adbario]

Thanks for the PR. 2.x needs to support PHP all the way down to version 5.5, so this needs a bit of investigation and testing. I've just done the change from Travis to Github actions for 2.x and will test these changes out asap.

[adbario]

Couldn't find any issues and all tests are running fine.

Thanks for your help with this project 🚀