Restore missing T_FN backfill test

Author: gsherwood

tests/Core/Tokenizer/BackfillFnTokenTest.php

@@ -632,6 +632,7 @@ public function dataNotAnArrowFunction()
                 '/* testNonArrowObjectMethodCallUpper */',
                 'FN',
             ],
+            ['/* testNonArrowNamespaceOperatorFunctionCall */'],
             ['/* testLiveCoding */'],
         ];