Add PHP 8.0 on GitHub action and Fix Psalm issue

[peter279k]

Description

Fix and improve some stuffs.

Motivation and context

• Adding the php-8.0 version test on GitHub action because this framework supports. And it should be verified.
• Fixing static analysis issue via Psalm:

Scanning files...
Analyzing files...

░░░░░░E░░░░░

ERROR: UnnecessaryVarAnnotation - src/MiddlewarePipeline.php:56:30 - The @var Psr\Http\Server\MiddlewareInterface annotation for $middleware is unnecessary (see https://psalm.dev/212)
                    /** @var MiddlewareInterface $middleware */


ERROR: UnnecessaryVarAnnotation - src/MiddlewarePipeline.php:87:30 - The @var Antidot\Application\Http\Middleware\MiddlewareQueue annotation for $queue is unnecessary (see https://psalm.dev/212)
                    /** @var MiddlewareQueue $queue */


------------------------------
2 errors found
------------------------------
13 other issues found.
You can display them with --show-info=true
------------------------------
Psalm can automatically fix 2 of these issues.
Run Psalm again with 
--alter --issues=UnnecessaryVarAnnotation --dry-run
to see what it can fix.
------------------------------

Checks took 6.79 seconds and used 303.539MB of memory
Psalm was able to infer types for 100% of the codebase
-----------------
100.000% src/Child.php (0 mixed)
100.000% src/Container/Config/ConfigProvider.php (0 mixed)
100.000% src/DriftKernelAdapter.php (0 mixed)
100.000% src/LoopFactory.php (0 mixed)
100.000% src/MiddlewarePipeline.php (0 mixed)
100.000% src/PromiseResponse.php (0 mixed)
100.000% src/ReactApplication.php (0 mixed)
100.000% src/ReactApplicationFactory.php (0 mixed)
100.000% src/RunServerCommandFactory.php (0 mixed)
100.000% src/ServerFactory.php (0 mixed)
100.000% src/SocketFactory.php (0 mixed)
100.000% src/WatchServerCommandFactory.php (0 mixed)

How has this been tested?

N/A

Screenshots (if appropriate)

N/A

Types of changes

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Improvements

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[kpicaza]

Nice improvement, thanks 💯