Update Windows builds to Qt 6.8.3 with matching MinGW toolchain

[ChungKelsey]

Summary

• update Windows builds from Qt 6.2.4 to Qt 6.8.3
• install Qt's matching MinGW 13.1 toolchain
• use mingw32-make explicitly in build and release workflows

Motivation

Qt 6.2.4 contains a multi-monitor screen detection regression that can
cause menus to open on the wrong display when identical monitor models
are connected.

The initial Qt 6.8.3 update in #361 failed in GitHub Actions with:

undefined reference to `__imp___argc`

The workflow installed Qt's MinGW binaries but compiled with the GitHub
runner's unrelated GCC 14.2 toolchain. This mixed incompatible MinGW
runtime and import libraries.

Installing the MinGW 13.1 toolchain supplied for Qt 6.8.3 and invoking
its mingw32-make keeps Qt, GCC, and the MinGW runtime ABI aligned.

Validation

• parsed both modified workflow files as YAML
• verified both Windows jobs install qt.tools.win64_mingw1310
• verified both Windows jobs invoke mingw32-make
• ran git diff --check

Supersedes #361.

Credit to @hendorog for the original Qt 6.8.3 update in #361.

[jankae]

Awesome, thank you for figuring this out! Somehow I did not think about another toolchain version at all and just figured jurplel/install-qt-action would install everything required for the specified Qt version.

[ChungKelsey]

I'm glad that help.