Don't test insert then read on sharded clusters in #fs test, write concern is not set

Author: estolfo

spec/mongo/database_spec.rb

@@ -322,7 +322,7 @@
     end
   end
 
-  describe '#fs' do
+  describe '#fs', unless: sharded? do
 
     let(:database) do
       described_class.new(authorized_client, TEST_DB)