Flush Housekeeping data from Redis specs

These specs use raw Redis objects which can not use the memory based
caching mechanism used for tests. As such we have to explicitly flush
the data from Redis before/after each spec to ensure no data lingers on.

spec/services/git_push_service_spec.rb

@@ -538,9 +538,16 @@ describe GitPushService, services: true do
     let(:housekeeping) { Projects::HousekeepingService.new(project) }
 
     before do
+      # Flush any raw Redis data stored by the housekeeping code.
+      Gitlab::Redis.with { |conn| conn.flushall }
+
       allow(Projects::HousekeepingService).to receive(:new).and_return(housekeeping)
     end
 
+    after do
+      Gitlab::Redis.with { |conn| conn.flushall }
+    end
+
     it 'does not perform housekeeping when not needed' do
       expect(housekeeping).not_to receive(:execute)