Nightly Installer Build

These get auto generated every few days. They get some basic testing in CI first, so the basics are guaranteed to work.

• msys2-x86_64-.exe: The GUI installer
• msys2-base-x86_64-*.sfx.exe: Just the files in a self extracting archive (missing Windows integration like shortcuts, uninstall entry, but otherwise works the same)
• msys2-base-x86_64-*.tar.zst: Same as .sfx.exe but as an ZSTD archive
• msys2-base-x86_64-*.tar.xz: Same as .sfx.exe but as an XZ archive
• msys2-base-x86_64-*.packages.txt: List of included packages and their versions