Upgrade PHPStan to 1.11.6

[westonruter]

This upgrades PHPStan to 1.11.6 which introduced two new issues.

 ------ -------------------------------------------------------------------------------------------------------------------- 
  Line   plugins/image-prioritizer/class-image-prioritizer-background-image-styled-tag-visitor.php                           
 ------ -------------------------------------------------------------------------------------------------------------------- 
  44     Offset 'background_image' might not exist on array{0?: string, 1?: string, background_image?: string, 2?: string}.  
 ------ -------------------------------------------------------------------------------------------------------------------- 

This is a case where PHPStan is not aware that at this point, the array keys are actually not nullable at this point. This is a bug in PHPStan which I've filed as phpstan/phpstan#11262. The issue seems to be that if the return value of preg_match() is casted to a bool or int then the array shape doesn't come through. So it's now checking to see if the return value is exactly 1 instead. Additionally, another check for '' !== $matches['background_image'] will be able to be removed once phpstan/phpstan#11222 is implemented, since we'll know that the array shape here has a non-empty-string.

 ------ ----------------------------------------------------------------- 
  Line   plugins/webp-uploads/hooks.php                                   
 ------ ----------------------------------------------------------------- 
  547    Variable $class_name in empty() always exists and is not falsy.  
 ------ -----------------------------------------------------------------

There was addressing the second if statement in the following code:

performance/plugins/webp-uploads/hooks.php

Lines 542 to 549 in b71d0a0

	// Find the ID of each image by the class.
	if ( ! preg_match( '/wp-image-([\d]+)/i', $img, $class_name ) ) {
	continue;
	}
	if ( empty( $class_name ) ) {
	continue;
	}

It is a useless condition because since preg_match() is known to have succeeded, the $class_name will never be empty.

This fixes the issue by removing that condition, but also makes the code more robust by leveraging the HTML Tag Processor. It also adds missing test assertions for webp_uploads_update_image_references().

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

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[westonruter]

This is more robust than before since it constraints looking for the class name inside the class attribute. Previously the string could be anywhere in the img tag.

[westonruter]

This will never be zero because the regex is now [1-9]\d*.

[adamsilverstein]

or, switch to using the wp_content_img_tag filter? #1259

[adamsilverstein]

Looks good! some test failing?

[westonruter]

@adamsilverstein I re-ran the failed jobs. They're passing now. Seems like a wp-env hiccup.

[adamsilverstein]

Spiffy!

[westonruter]

Bah. I should have removed the comment as it is now irrelevant after 75cd653 per phpstan/phpstan#11262 (comment). I'll do so as part of another PR.