Improve tests, asserions, CI setting and etc

[peter279k]

Changed log

• Fix Psalm analysis error
• Removing some comment annotations because they're unused.
• Adding the pull_request trigger to let upcoming PR can do GitHub Action work automatically.
• Fixing the AnnotationTest class namespace.
• Using the assertCount to assert expected count is same as result.
• To fix following Composer error, using the php-7.2 version to update cached dependencies:

Your lock file does not contain a compatible set of packages. Please run composer update.

  Problem 1
    - ocramius/package-versions is locked to version 1.4.2 and an update of this package was not requested.
    - ocramius/package-versions 1.4.2 requires composer-plugin-api ^1.0.0 -> found composer-plugin-api[2.0.0] but it does not match the constraint.
  Problem 2
    - ocramius/package-versions 1.4.2 requires composer-plugin-api ^1.0.0 -> found composer-plugin-api[2.0.0] but it does not match the constraint.
    - vimeo/psalm 3.12.1 requires ocramius/package-versions ^1.2 -> satisfiable by ocramius/package-versions[1.4.2].
    - vimeo/psalm is locked to version 3.12.1 and an update of this package was not requested.

ocramius/package-versions only provides support for Composer 2 in 1.8+, which requires PHP 7.4.
If you can not upgrade PHP you can require composer/package-versions-deprecated to resolve this with PHP 7.0+.

[peter279k]

To fix following Psalm error, using the @return bool|int|float|string annotation:

ERROR: InvalidReturnType - src/Compiler/Specification.php:30:16 - The declared return type 'bool|float|string' for Mill\Compiler\Specification::convertSampleDataToCompatibleDataType is incorrect, got 'scalar' (see https://psalm.dev/011)
     * @return bool|float|string

[peter279k]

To fix following Psalm error:

ERROR: UnsafeInstantiation - tests/Parser/Annotations/AnnotationTest.php:32:18 - Cannot safely instantiate class Mill\Parser\Annotation with "new $class_name" as its constructor might change in child classes (see https://psalm.dev/229)
                (new $annotation($this->getApplication(), $content, __CLASS__, __METHOD__))->process();

[peter279k]

BTW, it can also use the @psalm-consistent-constructor annotation for the abstract Annotation class.

And it's up to the repository owner.