Cells: Fix cross-joins arising from members (app/models/group.rb)

Description

All cross-joins that are currently allowed to pass that arises from members should be fixed. They are marked in the codebase with allow_cross_joins_across_databases(url: "https://gitlab.com/gitlab-org/gitlab/-/issues/422405").

• app/models/group.rb:42: .allow_cross_joins_across_databases(url: "#422405 (closed)")

Refer to the epic for more information about this. Be aware of #428105.

Related to #422405 (closed).