minor symfony#58751 [Process] fix the constant being used (xabbuh)

This PR was merged into the 5.4 branch.

Discussion
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[Process] fix the constant being used

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        |
| License       | MIT

Commits
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b811c1a fix the constant being used

Author: nicolas-grekas

src/Symfony/Component/Process/Tests/ExecutableFinderTest.php

@@ -157,7 +157,7 @@ public function testEmptyDirInPath()
             $finder = new ExecutableFinder();
             $result = $finder->find('executable');
 
-            $this->assertSame(sprintf('.%sexecutable', \PATH_SEPARATOR), $result);
+            $this->assertSame(sprintf('.%sexecutable', \DIRECTORY_SEPARATOR), $result);
         } finally {
             unlink('executable');
         }