unskip the niri nonlinearity test. There is a specific refs for release/4.x, I want to confirm that it works.

Author: KathleenLabrie

geminidr/niri/tests/test_nonlinearity_correct.py

@@ -15,7 +15,6 @@
 
 datasets = ["N20070819S0104_varAdded.fits"]
 
-@pytest.mark.skip("skip temporarily")
 @pytest.mark.niri
 @pytest.mark.parametrize("ad", datasets, indirect=True)
 @pytest.mark.preprocessed_data