Implement PHP 8.1's ArrayAccess interface

[grantholle]

PHP 8.1 enforces return types for ArrayAccess implementations.

Please take note of our contributing guidelines: https://docs.laravel-excel.com/3.1/getting-started/contributing.html
Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.

1️⃣ Why should it be added? What are the benefits of this change?

PHP 8.1 Support

2️⃣ Does it contain multiple, unrelated changes? Please separate the PRs out.

No

3️⃣ Does it include tests, if possible?

No

4️⃣ Any drawbacks? Possible breaking changes?

I believe that the minimum version PHP 7.2 should be ok, but can't say for certain.

5️⃣ Mark the following tasks as done:

• Checked the codebase to ensure that your feature doesn't already exist.
• Take note of the contributing guidelines.
• Checked the pull requests to ensure that another person hasn't already submitted a fix.
• Added tests to ensure against regression.
• Updated the changelog

6️⃣ Thanks for contributing! 🙌

[patrickbrouwers]

Thanks 👍

Running the change against all PHP versions now

[grantholle]

It looks like mixed is getting scoped weird. I think I need to change it to \mixed?

[patrickbrouwers]

Hm that's annoying, I'm afraid that is a breaking change that will have to result into dropping support for PHP7.x Let me think about this first.

[patrickbrouwers]

Think I found a way by using #[\ReturnTypeWillChange]

[grantholle]

Great!