[CI] Include a no-plot run
[CI] Include a no-plot run

This is because this type of run shall succeed regardless of how
examples are coded and if they generate errors and even for the case for
known failing examples which are accepted to fail and here they shall
not manifest themselves.

lesteve/sphinx-gallery,Eric89GXL/sphinx-gallery,sphinx-gallery/sphinx-gallery,lesteve/sphinx-gallery,Titan-C/sphinx-gallery,Titan-C/sphinx-gallery,Eric89GXL/sphinx-gallery,sphinx-gallery/sphinx-gallery