1.6.6 -> 1.9 regression: "unexpected token" error for the "`" signs delimiting the when incremental clause

[BenBirt]

https://dataform-users.slack.com/archives/CHMJK8MKM/p1597944866009900

[BenBirt]

config {
  type: "incremental",
}
SELECT
  *
FROM
  EXTERNAL_QUERY(
    "<external postgres db>",
    """
    SELECT
      id,
      updated_at
    FROM
      <some table>
    ${when(incremental(), `WHERE updated_at >= CURRENT_DATE - 1`)}
    """
  )