Ignore unset PHPStan errors in phpstan.neon.

Closes #3432556

active_filters.module

@@ -173,11 +173,8 @@ function template_preprocess_active_filters(array &$variables): void {
   ]);
 
   unset(
-    // @phpstan-ignore-next-line
     $variables['content_attributes'],
-    // @phpstan-ignore-next-line
     $variables['title_prefix'],
-    // @phpstan-ignore-next-line
     $variables['title_suffix'],
   );
 }
@@ -268,13 +265,9 @@ function template_preprocess_active_filter(array &$variables): void {
   $variables['wrapper_attributes'] = new Attribute();
 
   unset(
-    // @phpstan-ignore-next-line
     $variables['content_attributes'],
-    // @phpstan-ignore-next-line
     $variables['title_attributes'],
-    // @phpstan-ignore-next-line
     $variables['title_prefix'],
-    // @phpstan-ignore-next-line
     $variables['title_suffix'],
   );
 }
@@ -309,13 +302,9 @@ function template_preprocess_active_filter_group(
   ]);
 
   unset(
-    // @phpstan-ignore-next-line
     $variables['content_attributes'],
-    // @phpstan-ignore-next-line
     $variables['title_attributes'],
-    // @phpstan-ignore-next-line
     $variables['title_prefix'],
-    // @phpstan-ignore-next-line
     $variables['title_suffix'],
   );
 }