fix grammar issue in a comment (#10269)

Fixed some syntax errors in the comments

src/server.c

@@ -1273,7 +1273,7 @@ int serverCron(struct aeEventLoop *eventLoop, long long id, void *clientData) {
         }
     }
     /* Just for the sake of defensive programming, to avoid forgetting to
-     * call this function when need. */
+     * call this function when needed. */
     updateDictResizePolicy();