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.

spec/components/email/processor_spec.rb

@@ -5,7 +5,7 @@ require "email/processor"
 
 describe Email::Processor do
   after do
-    Discourse.redis.flushall
+    Discourse.redis.flushdb
   end
 
   let(:from) { "foo@bar.com" }