[3.0] CI: update Windows LLVM UCRT image to LLVM 19

Based on Debian trixie and contains mingw-w64 v13.

It's used for the Windows arm64 builds.

Since we are about to release the first official binaries, let's start with a recent toolchain.

libbluray 1.4.0 requires meson but it doesn't build with meson 0.56 so we need the same python+meson update as in !7640 (merged)