Add MinGW GCC CI coverage

[danyalahmed1995]

Closes #2584.

Adds a dedicated Windows x64 MinGW GCC CI job using MSYS2 UCRT64.

The job:

• installs the MinGW GCC toolchain through MSYS2
• verifies the selected compiler and target
• generates the Vulkan-Hpp headers
• builds the samples and tests with C++23 module support enabled
• runs the test suite

Fork validation

The validation run completed with 27 passing checks and two failures:

• Windows x64, MinGW GCC, Ninja

  • reproduces the known MinGW GCC module linker failure tracked in Having to patch vulkan.hpp when using vulkan.cppm with WinLibs GCC #2468
  • fails with duplicate definitions of the function-local errorCategory instance

• ubuntu-24.04 x64, Ninja, clang++-18

  • this is an existing matrix job and is separate from the newly added MinGW job

The MinGW failure is intentionally left visible as a toolchain signal. As discussed in #2596, the existing Vulkan-Hpp implementation is valid and links successfully with MSVC and Clang, so this PR does not add a project-side workaround for the MinGW GCC bug.

Refs #2468.

[sharadhr]

@asuessenbach that particular CI is meant to fail; see #2468. I think it is ready for merge otherwise.

[asuessenbach]

that particular CI is meant to fail; see #2468.

I know. And I'll merge it as soon as the root cause of failure is resolved.