Switch to Qt 6.11.1 or later

[yukawa]

Description

Qt 6.11.1 is expected to be released on April 30, 2026. Let's update to Qt 6.11.1 or later when it becomes available.

• https://wiki.qt.io/Qt_6.11_Release#Qt_6.11_release_plan

The main motivation of updating Qt version is for the better support of latest macOS build toolchain.

• build_qt.py fails with Xcode 26.4 on macOS #1455

It's also a relatively long time since we last updated Qt version. Currently we are using Qt 6.9.1, which was released on June 3, 2025.

Version or commit-id

395f9d7