style: Fix the issue of inconsistent menu spacing. (#7932)

Author: ssongliu

frontend/src/layout/components/Sidebar/index.scss

@@ -51,6 +51,7 @@
             background-color: var(--el-menu-item-bg-color);
             box-shadow: 0 0 4px rgba(0, 94, 235, 0.1);
             height: 46px;
+            margin: 6px 0;
             border-radius: 4px;
             &:hover {
                 .el-icon {