🐛 Data-grid-react: fix test setup

[oddvernes]

Ever since data-grid-react was added, the pnpm test:data-grid-react command have in fact been pointing to the eds-core-react tests in the root package.json. Thus, the data-grid tests never ran on github-actions this whole time 😂 👍.
Turns out there is a problem with the tests as babel-plugin-styled-components is unable to resolve eds-core-react commonjs file.
It is a bit unclear to me if this plugin is even supposed to read this file?? (it is already parsed and transpiled by the same plugin in its own build step) So perhaps the solution lies in jest.config.ts. Hopefully it is not something wrong with the core-react build. Of course due to the lack of test being ran, it is unclear when this problem started in the first place, but most likely when we upgraded to styled-components v6, or after the major dependency update last release.

Anyway the specific problem causing test to crash lies in babel-plugin-styled-components/lib/utils/detectors.js from line 123 where tag.object is undefined, and could be fixed by adding null-checks here, but as I said I'm not sure the plugin is supposed to read this file 🤷‍♂