(core) Fix detach of summaries grouped by RefList.

Summary:
DetachSummaryViewSection meant to generate CONTAINS($col, match_empty=0) for
RefList group-bys, but due to a typo ("Reflist" vs "RefList"), it generated an
equality lookup instead and the detached table's group column (and therefore
all others) came out as TypeError cells.

Test Plan: Added a test case.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D5038