Fix AppCleaner test for cross-platform compatibility

The exclusive file lock used to force Directory.Delete failure only works on Windows.
On Linux, deletion succeeds anyway so adjust asserts to match platform behavior while still covering fallback on Windows.

Author: kzu

src/Tests/AppCleanerTests.cs

@@ -32,8 +32,17 @@ public void Clean_deletes_stamp_when_publish_directory_delete_fails()
         var exit = AppCleaner.Clean(root, stamp);
 
         Assert.Equal(0, exit);
-        Assert.True(Directory.Exists(root));
-        Assert.False(File.Exists(stamp));
+        if (OperatingSystem.IsWindows())
+        {
+            // Exclusive lock should cause Directory.Delete to fail, triggering stamp-only fallback
+            Assert.True(Directory.Exists(root));
+            Assert.False(File.Exists(stamp));
+        }
+        else
+        {
+            // On Unix, open file locks do not prevent directory deletion; dir (and stamp) are removed
+            Assert.False(Directory.Exists(root));
+        }
     }
 
     [Fact]