This prevents $TMPDIR from being littered with *-journal files
after running the test suite.
This shouldn't cause excessive memory use since $v2w->{mm_tmp}
doesn't see big transactions. There's no need to worry about
data loss, here,either, since this is just a temporary clone
we've even disabled fsync on.
Fixes: 78888d36fb80889f ("msgmap: use TRUNCATE for journal_mode, for now")
$self->{dbh}->sqlite_backup_to_file($fn);
my $tmp = ref($self)->new_file($fn, 1);
$tmp->{dbh}->do('PRAGMA synchronous = OFF');
+ $tmp->{dbh}->do('PRAGMA journal_mode = MEMORY');
$tmp->{tmp_name} = $fn; # SQLite won't work if unlinked, apparently
$tmp->{pid} = $$;
close $fh or die "failed to close $fn: $!";