Added support for PHP 8.1

[Koen1999]

Q	A
Documentation	no
Bugfix	no
BC Break	no
New Feature	yes
RFC	no
QA	no

Description

This PR adds support for PHP 8.1. No big changes had to be made luckily. I ran a code inspection indicating no compatibility issues. Moreover, all tests are passing.
This fixes #17

/bin/php8.1 /home/koen/laminas-mvc-plugin-flashmessenger/vendor/phpunit/phpunit/phpunit --configuration /home/koen/laminas-mvc-plugin-flashmessenger/phpunit.xml.dist /home/koen/laminas-mvc-plugin-flashmessenger/test --teamcity
Testing started at 19:31 ...
PHPUnit 9.5.10 by Sebastian Bergmann and contributors.



Time: 00:00.061, Memory: 8.00 MB

OK (47 tests, 195 assertions)
Process finished with exit code 0

[Koen1999]

Should I adjust the lock file such that it works with PHP 7.3 or what is your policy on this?

[snapshotpl]

Try to composer require php "^7.3 || ~8.0.0 || ~8.1.0" instead of composer update

[froschdesign]

@Koen1999
Please see the error:

https://github.com/laminas/laminas-mvc-plugin-flashmessenger/runs/4372224075?check_suite_focus=true#step:3:336

Add:

use ReturnTypeWillChange;

…

#[ReturnTypeWillChange]
public function getIterator()

[Ocramius]

Thanks @Koen1999!