Docs fail, CI passes

In the latest main commit, the documentation fails to build the tutorial Operations and Qubits. See, for example, version 0.9.0 here.

Two issues with this:

1. We should fix the tutorial (and include this fix in the next patch release).
2. The CI should not pass if part of the documentation fails to build.

Tagging @gdenes for the tutorial and @slavoutich for the CI.