Ensure artist insights flex container uses 100% of available space
Ensure artist insights flex container uses 100% of available space

Fixes the following issue found during QA:

> Upon clicking "X more" link, the column seems to shift to the right
> slightly. See recording: https://cl.ly/4d787cb60e0d

ticket: https://artsyproduct.atlassian.net/browse/DISCO-676

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