Ensured that our django checkout is in the pythonpath during tests.

This fixes an issue with postgres_tests.test_integration.PostgresIntegrationTests
which would not find Django in a CI run.

tests/postgres_tests/test_integration.py

@@ -7,11 +7,16 @@ from . import PostgreSQLSimpleTestCase
 
 class PostgresIntegrationTests(PostgreSQLSimpleTestCase):
     def test_check(self):
+        test_environ = os.environ.copy()
+        if 'DJANGO_SETTINGS_MODULE' in test_environ:
+            del test_environ['DJANGO_SETTINGS_MODULE']
+        test_environ['PYTHONPATH'] = os.path.join(os.path.dirname(__file__), '../../')
         result = subprocess.run(
             [sys.executable, '-m', 'django', 'check', '--settings', 'integration_settings'],
             stdout=subprocess.DEVNULL,
             stderr=subprocess.PIPE,
             cwd=os.path.dirname(__file__),
+            env=test_environ
         )
         stderr = '\n'.join([e.decode() for e in result.stderr.splitlines()])
         self.assertEqual(result.returncode, 0, msg=stderr)