Update PHPStan level to 2

[westonruter]

See #775.

This fixes the following PHPStan issues:

 ------ -------------------------------------------------------------------- 
  Line   plugins/dominant-color-images/helper.php                            
 ------ -------------------------------------------------------------------- 
  76     Call to an undefined method WP_Image_Editor::has_transparency().    
  82     Call to an undefined method WP_Image_Editor::get_dominant_color().  
 ------ -------------------------------------------------------------------- 

Note that PHPStan is correctly identifying a bug here which could cause a fatal error in case another plugin is filtering wp_image_editors so that our specific subclasses are not used.

[github-actions]

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Co-authored-by: westonruter <westonruter@git.wordpress.org>
Co-authored-by: mukeshpanchal27 <mukesh27@git.wordpress.org>

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[mukeshpanchal27]

Suggested change

	/**
	/*

Seems it's local variable so do we needs to use multiline comment per https://developer.wordpress.org/coding-standards/inline-documentation-standards/php/#5-inline-comments

[westonruter]

I don't think that's right. Without /** then the phpdoc is not parsed.

[westonruter]

The docs you link to are talking about a regular multiline comment, not one that serves as a doc block.