fix test

Signed-off-by: Alex Chi <iskyzh@gmail.com>

rust/frontend/test_runner/tests/testdata/mv_on_mv.yaml

@@ -10,7 +10,7 @@
   sql: |
     select m1.v1 as m1v1, m1.v2 as m1v2, m2.v1 as m2v1, m2.v2 as m2v2 from m1 join m2 on m1.v1 = m2.v1;
   stream_plan: |
-    StreamMaterialize { columns: ["m1v1", "m1v2", "m2v1", "m2v2", "expr#4"(hidden), "expr#5"(hidden)], pk_columns: ["expr#4", "expr#5"] }
+    StreamMaterialize { columns: [m1v1, m1v2, m2v1, m2v2, expr#4(hidden), expr#5(hidden)], pk_columns: [expr#4, expr#5] }
       StreamProject { exprs: [$0, $1, $3, $4, $2, $5], expr_alias: [m1v1, m1v2, m2v1, m2v2,  ,  ] }
         StreamHashJoin { type: Inner, predicate: $0 = $3 }
           StreamExchange { dist: HashShard([0]) }