SourcesModal: Add title variant short attribution to tab labels (if needed)

[sophiamersmann]

Description

• The tab labels currently show the title_public as label
• This is usually ok, but sometimes the public title is the same for all indicators, which means that all labels have the same title

Expected behaviour

Add the title_variant and attribution_short to the tab labels. Not sure if we always want to do this or only when necessary.

Screenshots

Related

Another issue about tab labels: https://github.com/owid/owid-grapher/issues/3654. To solve both, we probably want to make tab labels multi line.