Isolate each specs for cache store (#6450)

The cache store is explicitly used by some specs, but they were not
isolated and therefore not reliable. This fixes the issue by clearing
the cache after each specs.

spec/models/setting_spec.rb

@@ -42,11 +42,6 @@ RSpec.describe Setting, type: :model do
         described_class[key]
       end
 
-      it 'calls Rails.cache.fetch' do
-        expect(Rails).to receive_message_chain(:cache, :fetch).with(cache_key)
-        described_class[key]
-      end
-
       context 'Rails.cache does not exists' do
         before do
           allow(RailsSettings::Settings).to receive(:object).with(key).and_return(object)
@@ -103,6 +98,14 @@ RSpec.describe Setting, type: :model do
           Rails.cache.write(cache_key, cache_value)
         end
 
+        it 'does not query the database' do
+          expect do |callback|
+            ActiveSupport::Notifications.subscribed callback, 'sql.active_record' do
+              described_class[key]
+            end
+          end.not_to yield_control
+        end
+
         it 'returns the cached value' do
           expect(described_class[key]).to eq cache_value
         end