Update the value of the `diffEnd` when click `Show More` btn in the DiffFileTree (#24069) (#24078)

Backport #24069 by @sillyguodong

In the component `DiffFileTree`,if don't update the value of the
`diffEnd` in the callback of ajax request, click `Show More` btn will
always return the same response, duplicate files are appended to the
file list.

Before:

https://user-images.githubusercontent.com/33891828/231371188-82d169af-10bb-47e2-8aca-83ced2597f2d.mov

After:

https://user-images.githubusercontent.com/33891828/231369805-39a5a4d0-662c-4f08-bc5a-7d31e8782453.mov

Co-authored-by: sillyguodong <33891828+sillyguodong@users.noreply.github.com>

web_src/js/components/DiffFileTree.vue

@@ -123,6 +123,8 @@ export default {
       this.isLoadingNewData = true;
       doLoadMoreFiles(this.link, this.diffEnd, () => {
         this.isLoadingNewData = false;
+        const {pageData} = window.config;
+        this.diffEnd = pageData.diffFileInfo.diffEnd;
       });
     },
   },