[ci] Reset the cache before each rspec suite

With things like database_cleaner you really want to make sure that
tests don't pollute each other with stale cache items

(rails defaults to null_store in test environment, but that's a
harsher measure)

src/api/spec/rails_helper.rb

@@ -69,3 +69,6 @@
 
 # support Delayed Jobs
 require 'support/delayed_job'
+
+# Cache reset
+require 'support/cache'

src/api/spec/support/cache.rb

@@ -0,0 +1,6 @@
+# reset the cache before each test
+RSpec.configure do |config|
+  config.before do
+    Rails.cache.clear
+  end
+end