Fix dirname failed test (#44510)

Author: alirezasalehizadeh

tests/Support/SupportStringableTest.php

@@ -178,14 +178,12 @@ public function testDirname()
     {
         $this->assertSame('/framework/tests', (string) $this->stringable('/framework/tests/Support')->dirname());
         $this->assertSame('/framework', (string) $this->stringable('/framework/tests/Support')->dirname(2));
+        $this->assertSame('.', (string) $this->stringable('framework')->dirname());
 
-        $this->assertSame('/', (string) $this->stringable('/framework/')->dirname());
-
-        $this->assertSame('/', (string) $this->stringable('/')->dirname());
         $this->assertSame('.', (string) $this->stringable('.')->dirname());
 
-        //  without slash
-        $this->assertSame('.', (string) $this->stringable('framework')->dirname());
+        $this->assertSame(DIRECTORY_SEPARATOR, (string) $this->stringable('/framework/')->dirname());
+        $this->assertSame(DIRECTORY_SEPARATOR, (string) $this->stringable('/')->dirname());
     }
 
     public function testUcsplitOnStringable()