[CI] Fix running examples by ignoring warnings

Matplotlib 3.6.0 introduced a new incidental warning which has nothing
to do with our code. This change ignores that warning so other warnings
can still be caught.

.github/workflows/main.yml

@@ -309,7 +309,8 @@ jobs:
           -exec sh -c 'for n; do echo "$n" | tee -a results.txt && python3 "$n" >> results.txt || exit 1; done' sh {} +
         env:
           PYTHONPATH: build/python
-          PYTHONWARNINGS: error
+          # The ignore setting here is due to a new warning introduced in Matplotlib==3.6.0
+          PYTHONWARNINGS: "error,ignore:warn_name_set_on_empty_Forward::pyparsing"
           MPLBACKEND: Agg
       - name: Save the results file for inspection
         uses: actions/upload-artifact@v2