Fix registry cache broken (#2715)

* services is shared between routines, when application change services returned by get function may lead to other routine set a changed services to cache

* services is shared between routines, when application change services returned by get function may lead to other routine set a changed services to cache

---------

Co-authored-by: Shuaihu Liu <shuaihu.liu@shopee.com>

registry/cache/cache.go

@@ -161,11 +161,12 @@ func (c *cache) get(service string) ([]*registry.Service, error) {
 		}
 
 		// cache results
+		cp := util.Copy(services)
 		c.Lock()
-		c.set(service, util.Copy(services))
+		c.set(service, services)
 		c.Unlock()
 
-		return services, nil
+		return cp, nil
 	}
 
 	// watch service if not watched