Replace nose2.main() with pytest.main().

Signed-off-by: Daniel Scheffler <danschef@gfz-potsdam.de>

tests/test_COREG.py

@@ -359,5 +359,5 @@ class CompleteWorkflow_INTER1_S2A_S2A(unittest.TestCase):
 
 
 if __name__ == '__main__':
-    import nose2
-    nose2.main()
+    import pytest
+    pytest.main()

tests/test_COREG_LOCAL.py

@@ -201,5 +201,5 @@ class CompleteWorkflow_INTER1_S2A_S2A(unittest.TestCase):
 
 
 if __name__ == '__main__':
-    import nose2
-    nose2.main()
+    import pytest
+    pytest.main()

tests/test_tie_point_grid.py

@@ -134,5 +134,5 @@ class Test_Tie_Point_Grid(unittest.TestCase):
 
 
 if __name__ == '__main__':
-    import nose2
-    nose2.main()
+    import pytest
+    pytest.main()