GH-130415: Narrow str to "" based on boolean tests (GH-130476)

Python/optimizer_bytecodes.c

@@ -426,7 +426,7 @@ dummy_func(void) {
 
     op(_TO_BOOL_STR, (value -- res)) {
         if (!optimize_to_bool(this_instr, ctx, value, &res)) {
-            res = sym_new_type(ctx, &PyBool_Type);
+            res = sym_new_truthiness(ctx, value, true);
             sym_set_type(value, &PyUnicode_Type);
         }
     }