[ci] Use custom sphinx-gallery in ci_gpu

[driazati]

To enable #10921 this builds sphinx-gallery using @guberti's changes. Patch was created via

git clone https://github.com/sphinx-gallery/sphinx-gallery.git
cd sphinx-gallery
curl -L https://github.com/sphinx-gallery/sphinx-gallery/pull/940.diff | patch -p1 -d .
curl -L https://github.com/sphinx-gallery/sphinx-gallery/pull/941.diff | patch -p1 -d .
git diff > sphinx_gallery_colab_fixes.patch

cc @areusch

[guberti]

Thanks for the patch @driazati! For completeness, it's worth noting I had to make a third change to sphinx-gallery to get Python notebooks working again (sphinx-gallery/sphinx-gallery#943). That change was merged last night though, so nothing needs to change with this PR.

[driazati]

closing for now since we're going to revisit how we handle tutorials in a more generic way and this will make updating versions more difficult