test: change database from within pre-new hook

test: change database from within pre-new hook

Due to the change in the config system, notmuch keeps a notmuch database
open when it would not do so before. Consequently, it can miss changes
to the database which are done from a hook (while notmuch holds the
databse in read only mode). When notmuch itself writes to the database
after that it uses wrong assumptions about the last used doc id etc.

Demonstrate this by triggering an assertion. (This new test succeeds
with notmuch 0.31.4.)

Signed-off-by: Michael J Gruber <git@grubix.eu>
Amended-by: db. Check for both messages