Install a missing python module for the swh-search build

Related to swh/infra/sysadm-environment#3484 (closed)

Test Plan

• make the docker image
• in the swh-search repo (be careful of the file permissions), run:

docker run -ti --rm -v /var/run/docker.sock:/var/run/docker.sock -v ~/wip/.arcrc:/home/jenkins/.arcrc -v /usr/bin/docker:/usr/bin/docker -u jenkins:docker --entrypoint bash -v /tmp/swh-search:/src --name jenkins swh-jenkins/tox
yarn install
yarn build

The build should be ok

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Migrated from D6085 (view on Phabricator)