Improve VariantsController request spec realism

For this endpoint use the q parameter with Ransack variant_search_term
has to be a falsy value/not exist. By default, variantAutocomplete has
variant_search_term defined and needs to be overriden if ransack wants
to be used.

api/spec/requests/spree/api/variants_spec.rb

@@ -47,7 +47,7 @@ module Spree::Api
 
  it 'can query the results through ransack' do
  expected_result = create(:variant, sku: 'FOOBAR')
- get spree.api_variants_path, params: { q: { sku_cont: 'FOO' } }
+ get spree.api_variants_path, params: { variant_search_term: nil, q: { sku_cont: 'FOO' } }
  expect(json_response['count']).to eq(1)
  expect(json_response['variants'].first['sku']).to eq expected_result.sku
  end