Add error logging for unlink failures

lib/gitlab/set_cache.rb

@@ -64,7 +64,9 @@ module Gitlab
       else
         redis.del(*keys)
       end
-    rescue ::Redis::CommandError
+    rescue ::Redis::CommandError => e
+      Gitlab::ErrorTracking.log_exception(e)
+
       redis.del(*keys)
     end
   end

spec/lib/gitlab/repository_set_cache_spec.rb

@@ -103,6 +103,12 @@ describe Gitlab::RepositorySetCache, :clean_gitlab_redis_cache do
         expect(cache.expire(:foo)).to eq(1)
         expect(cache.read(:foo)).to be_empty
       end
+
+      it 'logs the failure' do
+        expect(Gitlab::ErrorTracking).to receive(:log_exception)
+
+        cache.expire(:foo)
+      end
     end
   end