table组件 table column的sortable属性设置为custom无效

### Description

版本1.4.20

当设置table 组件的column 的sortable属性为custom时，期望不触发内部排序（目前是触发的前端排序），直接触发table的onSortChange方法。

### Reproduce Steps

### Error Trace (if possible)

It's better to post up the error stack for us to trace this issue.

源码table组件tableStore文件的changeSortCondition，没有对sortable为custom做特殊判断，进行了前端排序

### Solution

What needs to be done to address this issue? Ideally, provide a pull request with a fix.

### Additional Information

Any additional information, configuration or data that might be necessary to reproduce the issue.