Hack test case to unblock Oracle tests (#39317)

* Hack test case to unblock Oracle tests

In metabase.query-processor-test.implicit-joins-test/implicit-joins-with-expressions-test
we calculate an interval by going back from today a number of years to arrive at 2019. On
February 29, this calculation fails with Oracle because there was no February 29 in 2019.
This hack changes 2019 to 2020 and makes Oracle happy.
breakout-on-temporally-bucketed-implicitly-joined-column-inside-source-query-test
had to be adjusted too.