Require test fails on linux when path contains DIRECTORY_SEPARATOR #14944

Bug report

I use the following syntax to include files:

require __DIR__.DIRECTORY_SEPARATOR.'bootstrap.php';

After upgrading from 2.2.2 to 2.2.3, I get this phpstan error:

  8      Path in require() __DIR__ . \DIRECTORY_SEPARATOR . 'bootstrap.php' is  
         not a file or it does not exist.                                       
         🪪  require.fileNotFound          

This error only occurs on Linux, not on Windows.
require errors are hard to reproduce on the playground because there no files exist.
I created a PR with a modified test on phpstan/phpstan-src#6027 to demonstrate the problem. From the error message there is seems that on Linux DIRECTORY_SEPARATOR is a backslash.

I don't know why my version shows DIRECTORY_SEPARATOR in the error message and the test results of the PR show the resolved path.

Code snippet that reproduces the problem

phpstan/phpstan-src#6027

Expected output

No errors.

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