test: Update test_plot_results_no_axis baseline image (#2009)

* matplotlib v3.6.0 results in a slightly different baseline image than
  matplotlib v3.5.x, so regenerate the baseline image using matplotlib v3.6.0
  with `pytest --mpl-generate-path=tests/contrib/baseline tests/contrib/test_viz.py`.
* Mark the test_plot_results_no_axis test as xfail for Python 3.7 as matplotlib v3.6.0
  is Python 3.8+ and so the image is guaranteed to be different as Python 3.7 runtimes
  will install matplotlib v3.5.x.

tests/contrib/test_viz.py

@@ -1,4 +1,5 @@
 import json
+import sys
 
 import matplotlib
 import matplotlib.pyplot as plt
@@ -67,6 +68,10 @@ def test_plot_results(datadir):
 
 
 @pytest.mark.mpl_image_compare
+@pytest.mark.xfail(
+    sys.version_info < (3, 8),
+    reason="baseline image generated with matplotlib v3.6.0 which is Python 3.8+",
+)
 def test_plot_results_no_axis(datadir):
     data = json.load(datadir.joinpath("hypotest_results.json").open(encoding="utf-8"))