feat: support for php 8 style Test attribute

[lotyp]

Adds support for PHPUnit #[Test] attribute

Closes: #144

[weirdan]

There's a $method_storage->attributes property that contains the attributes as Psalm understood them. For example, it (should) include attributes from stub files. Thus it's better to use that rather than low-level PHPParser stuff.

[weirdan]

Also please add the variant with #[Test] into this test case:

psalm-plugin-phpunit/tests/acceptance/TestCase.feature

Lines 527 to 548 in e344eaa

	Scenario: Test method are never marked as unused
	Given I have the following code
	"""
	class MyTestCase extends TestCase
	{
	/**
	* @return void
	*/
	public function testSomething(int $int) {
	$this->assertEquals(1, $int);
	}
	/**
	* @return void
	* @test
	*/
	public function somethingElse(int $int) {
	$this->assertEquals(1, $int);
	}
	}
	"""
	When I run Psalm with dead code detection
	Then I see no errors