MNT some fixes for CircleCI v2
MNT some fixes for CircleCI v2

* use checkout in the deploy step
* tweaks to workspace persist/attach

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