@babel/core update breaks Gatsby site build

[daneah]

Expected behavior
Updating a patch version of @babel/core should be okay.

Actual behavior
Updating from 7.26.0 to 7.26.7 breaks the Gatsby site build.

Steps to reproduce the issue

1. run e.g. yarn upgrade-interactive and bump @babel/core
2. run yarn site:build
3. Observe an error regarding use of document in @ithaka/focus-trap that isn't available during SSR

Additional information
It's possible that resolving #777 will also fix this.