Autogen: Fix Ninja Multi-Config dependency graph regression

In commit 5363bebc1e (Autogen: Fix compilation of unchanged source files,
2024-07-16, v3.31.0-rc1~328^2) we relied on Ninja Multi-Config dependency graph
optimizations from commit 7c39dabdbc (Autogen: AUTO*_EXECUTABLE: add support
for per-config values, 2023-10-18, v3.29.0-rc1~105^2~1).  However, those graph
optimizations are conditional on versions of Qt that enable
[`AUTOGEN_BETTER_GRAPH_MULTI_CONFIG`](https://codereview.qt-project.org/c/qt/qtbase/+/513648).

`UseBetterGraph` should be checked to add ui files to `timestampByproducts`.

Fixes: #26475