test_catalogue_of_briefs_page_filtered: add london as second location selection
test_catalogue_of_briefs_page_filtered: add london as second location selection

so that we actually test multi-selection somewhere

alphagov/digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend