Update unit test's result messages

[spider-man-tm]

This PR is linked to the following issue:

close #1791

Current

Prepare the following table and its corresponding unit test.

Test table:

config {
    type: "table",
    schema: "hoge",
    name: "fuga"
}

select
  user_id
from
  ${ref("users")}

Test code:

config {
  type: "test",
  dataset: "fuga",
}

select 1 as user_id union all
select cast(null as int64) as user_id

input "users" {
  select 1 as user_id union all
  select 2 as user_id
}

Given that the expected block includes cast(null as int64), it would be more user-friendly to have the output display as follows:

For row 1 and column "user_id": expected null, but saw "2"

However, the current output is as follows, which can cause confusion for the user:

For row 1 and column "user_id": expected type "object", but saw type "number".

Before Committing

• Conducted unit testing
• Checked the behavior of dataform cli

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[Ekrekr]

I've run the tests, and all pass. Will merge, thanks for doing this!