Bug 14778: Mocks Koha::Database->_new_schema instead of C4::Context->_new_dbh

Bug 14778: Mocks Koha::Database->_new_schema instead of C4::Context->_new_dbh

C4::Context::_new_dbh does not exist anymore.
Koha::Database::_new_schema should be mocked instead.

Will fix:
- t/00-load.t
- t/Breeding.t
- t/ImportBatch.t
- t/Message.t
- t/Overdues.t
- t/Prices.t
- t/RotatingCollections.t
- t/Search.t
- t/SuggestionEngine_AuthorityFile.t
- t/XSLT.t

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>