Fixing bug with test broker_gen2

[knassre-bodo]

The actual defog SQL text is as follows:

SELECT COUNT(t.sbTxCustId) AS transaction_count
FROM sbTransaction AS t
JOIN sbCustomer AS c ON t.sbTxCustId = c.sbCustId
WHERE c.sbCustJoinDate >= date('now', '-70 days')

But the current PyDough implemnetation uses DATETIME("now", "-70 days") which does not truncate to the start of the day. To fix this, changed it to DATETIME("now", "-70 days", "start of day") so it is the same as the refsol.

[juankx-bodo]

LGTM. Lets wait for the CI tests to complete.