`readfile()` Windows test file can conflict with another test when run in parrallel

[Girgias]

Description

The following file ext\standard\tests\file\readfile_variation8-win32.phpt sometimes fails CI because warning about existing folder are issued by mkdir().

Can you have a look @cmb69 as you have a Windows machine?

PHP Version

master

Operating System

No response

[cmb69]

php-src/ext/standard/tests/file/readfile_variation9.phpt

Lines 8 to 9 in 7b8a61a

	$mainDir = "readfileVar8";
	$subDir = "readfileVar8Sub";