test: admin list view custom components (#10956)

### What?
This PR adds tests for custom list view components to the existing suite
in `admin/e2e/list-view/`. Custom components are already tested in the
document-level counterpart, and should be tested here as well.

### Why?
Previously, there were no tests for these list view components.
Refactors, features, or changes that impact the importMap, default list
view, etc., could affect how these components get rendered. It's safer
to have tests in place to catch this as custom list view components, in
general, are used quite often.

### How?
This PR adds 5 simple tests that check for the rendering of the
following list view components:
- `BeforeList`
- `BeforeListTable`
- `UI Field Cell`
- `AfterList`
- `AfterListTable`