Fix tests on WASI.

Author: serhiy-storchaka

Lib/test/test_posixpath.py

@@ -549,13 +549,19 @@ def test_realpath_invalid_paths(self):
             self.assertRaises(UnicodeDecodeError, realpath, path, strict=True)
         else:
             self.assertEqual(realpath(path, strict=False), path)
-            self.assertRaises(FileNotFoundError, realpath, path, strict=True)
+            if support.is_wasi:
+                self.assertRaises(FileNotFoundError, realpath, path, strict=True)
+            else:
+                self.assertRaises(OSError, realpath, path, strict=True)
         path = b'/nonexistent/\xff'
         if sys.platform == 'win32':
             self.assertRaises(UnicodeDecodeError, realpath, path, strict=False)
         else:
             self.assertEqual(realpath(path, strict=False), path)
-        self.assertRaises(FileNotFoundError, realpath, path, strict=True)
+        if support.is_wasi:
+            self.assertRaises(FileNotFoundError, realpath, path, strict=True)
+        else:
+            self.assertRaises(OSError, realpath, path, strict=True)
 
     @os_helper.skip_unless_symlink
     @skip_if_ABSTFN_contains_backslash