ReadTheDocs builds are failing

[manics]

ReadTheDocs builds are failing, see

• Added target="_blank"to nbviewer link so it doesn't take you away #1307
• https://readthedocs.org/projects/binderhub/builds/13998777/

A new version of MySt parser was released today, but that might just be coincidence. The previous RTD build was 11 days ago so it could well be that something else was updated.

Once the problem is been identified it might be worth pinning the doc dependencies exactly and relying on dependabot to bump them?

[consideRatio]

Perhaps because sphinx 4 is out since may 9th? No because a build has succeeded since then.

[minrk]

fixed by #1310