Bug 18749 - xt/sample_notices.t fails

Bug 18749 - xt/sample_notices.t fails

Bug Description:
When performing a unit test on xt/sample_notices.t with the command
'prove xt/sample_notices.t' 11 tests fail with the error message
"No sample notice to delete".

Cause of bug:
The failures are caused by an incorrect file path on Line 25 of
xt/sample_notices.t.

Patch Description:
This patch corrects the failures by changing $base_notices_file from
"en/default/sample_notices.sql" to "en/mandatory/sample_notices.sql"

Test Plan:
1) Drop into koha-shell and run the command 'prove xt/sample_notices.'
2) 11 unit tests fail.
3) Apply the patch.
4) Re-run 'prove xt/sample_notices.t'
5) All of the tests pass now.
6) Quit out of koha-shell

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>