[Tests only] Add Locator#locate_many tests for non id primary keys

[nvasilevski]

locate_many with ignore_missing: true used to be broken due to to id: values clause being hardcoded

globalid/lib/global_id/locator.rb

Line 145 in 5c68d15

model_class.where(id: ids)

We changed it in #163 which made it possible to fully support non-id named primary keys in locate_many

globalid/lib/global_id/locator.rb

Line 161 in 5ce154c

model_class.where(model_class.primary_key => ids)