minor #51096 Use more "First class callable syntax" + Normalize set_error_handler/set_exception_handler calls (lyrixx)

This PR was merged into the 6.4 branch.

Discussion
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Use more "First class callable syntax" + Normalize set_error_handler/set_exception_handler calls

| Q             | A
| ------------- | ---
| Branch?       | 6.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       |
| License       | MIT
| Doc PR        |

Commits
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be1bbbccc1 Use more "First class callable syntax" + Normalize set_error_handler/set_exception_handler calls

Author: nicolas-grekas

Filesystem.php

@@ -749,7 +749,7 @@ private static function box(string $func, mixed ...$args): mixed
         self::assertFunctionExists($func);
 
         self::$lastError = null;
-        set_error_handler(__CLASS__.'::handleError');
+        set_error_handler(self::handleError(...));
         try {
             return $func(...$args);
         } finally {