Run most recent PHP versions in the pipeline

That ensures we have support for the most recent versions.

I removed the PHPT files from the list of files PHPStan checks. That's
because I want to convert the PHPT files into Pest files, so it runs
faster with a better way of debugging things.

Author: henriquemoody

.github/workflows/continuous-integration.yml

@@ -15,6 +15,9 @@ jobs:
         php-version:
           - "8.1"
           - "8.2"
+          - "8.3"
+          - "8.4"
+          - "8.5"
 
     steps:
       - name: Checkout

phpstan.neon.dist

@@ -5,4 +5,3 @@ parameters:
     - tests/
   fileExtensions:
     - php
-    - phpt

tests/integration/stringify-declared.phpt

@@ -5,15 +5,17 @@ declare(strict_types=1);
 
 require 'vendor/autoload.php';
 
+use Respect\Stringifier\Helpers\ObjectHelper;
+
 outputMultiple(
     Traversable::class,
     ArrayIterator::class,
     BasicEnumeration::class,
-    Respect\Stringifier\Helpers\ObjectHelper::class,
+    ObjectHelper::class,
 );
 ?>
 --EXPECT--
 `Traversable`
 `ArrayIterator`
 `BasicEnumeration`
-`Respect\Stringifier\Helpers\ObjectHelper`
+`Respect\Stringifier\Helpers\ObjectHelper`