setting STARDOG_EXT breaks tests

[scardena]

see

pystardog/test/test_admin_basic.py

Line 370 in 51087bd

class TestLoadData(TestStardog):

.
These tests are broken when STARDOG_EXT is set. we should pack whatever driver required for the tests in docker-compose.
Also this test is duplicated:

pystardog/test/test_admin_basic.py

Line 554 in 51087bd

def test_materialize_graph_from_file(self, admin, db, conn):

We might want to check whether other tests are duplicated