reach a minimum of 80% SLOC coverage across all components

Here are the remaining components below thresholds, as of the last update of this task:

|----------------------+----------+------------|
| repository           | line (%) | branch (%) |
|----------------------+----------+------------|
| swh-web (frontend)   |       71 |         52 |

Source: https://jenkins.softwareheritage.org/view/swh%20master/

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Migrated from T1411 (view on Phabricator)