DEV: Change use of Redis flushall to flushdb.

FLUSHALL removes all keys from all databases. Instead we only want to
remove keys from the current Redis database.

plugins/discourse-narrative-bot/spec/discourse_narrative_bot/track_selector_spec.rb

@@ -472,7 +472,7 @@ describe DiscourseNarrativeBot::TrackSelector do
           let(:post) { Fabricate(:post, topic: topic) }
 
           after do
-            Discourse.redis.flushall
+            Discourse.redis.flushdb
           end
 
           describe 'when random reply massage has been displayed in the last 6 hours' do