teuthology/schedule.py: update parsed_yaml with base_config

teuthology/schedule.py: update parsed_yaml with base_config

In `schedule_suite` method,
`self.base_config` gets updated many times while backtracking
when using "--newest" flag. These changes were never updated
to `parsed_yaml` (job yaml) in `configs`.
As `configs` is intialised before backtracking.

Before, we used to write base_config to a tmp
file and pass that to teuthology-schedule
which used to take care of updates to base_config.
But this logic was removed in https://github.com/ceph/teuthology/pull/2008/files
so the updates to base_config then never make
it to job yaml anymore.

Fixes: https://tracker.ceph.com/issues/71612
Signed-off-by: Vallari Agrawal <val.agl002@gmail.com>