fix: expandIcon slot of BasicTable component is invalid (#975)

src/components/Table/src/BasicTable.vue

@@ -211,7 +211,7 @@
           // ...(dataSource.length === 0 ? { getPopupContainer: () => document.body } : {}),
           ...attrs,
           customRow,
-          expandIcon: expandIcon(),
+          expandIcon: slots.expandIcon ? null : expandIcon(),
           ...unref(getProps),
           ...unref(getHeaderProps),
           scroll: unref(getScrollRef),