Fix incorrect redirection when creating a PR fails (#29537)

This is only a quick fix to make it easier to backport.

After this PR gets merged, I will propose a new PR to fix the FIXME.

<details>

![image](98d1d5c4-2e79-4a75-80e9-76fd898986e0)

</details>

routers/web/repo/pull.go

@@ -1501,7 +1501,7 @@ func CompareAndPullRequestPost(ctx *context.Context) {
 				return
 			}
 			ctx.Flash.Error(flashError)
-			ctx.JSONRedirect(pullIssue.Link()) // FIXME: it's unfriendly, and will make the content lost
+			ctx.JSONRedirect(ctx.Link + "?" + ctx.Req.URL.RawQuery) // FIXME: it's unfriendly, and will make the content lost
 			return
 		}
 		ctx.ServerError("NewPullRequest", err)