Fix test (kernel died)

[thomasht86]

I confirm that this contribution is made under the terms of the license found in the root directory of this repository's source tree and that I have the authority necessary to make this contribution on behalf of its copyright owner.

2 changes:

1. Add vespacli to notebook_requirements.txt, so it gets pre-installed on test-runners, reducing execution time of each notebook.
2. Try to fix strange test failure while running https://pyvespa.readthedocs.io/en/latest/examples/Matryoshka_embeddings_in_Vespa-cloud.html by reducing memory usage.

Test fails with

08:04:58 nbclient.exceptions.DeadKernelError: Kernel died 

on some of the cells right after Cloud deployment.

This error usually occurs due to exceeding memory resources. It is still strange that this would only occur now, with unchanged resource specs. 🤔

[jobergum]

💯