fix(ci): Ruby build-from-source fails on Windows with newer MinGW/GCC toolchains

[CalvinAllen]

Problem

The build-ruby-from-source workflow fails when compiling older Ruby versions (e.g., 3.2.10) on Windows using MSYS2/MinGW. The newer GCC 15.x toolchain in MSYS2 produces incompatible pointer type errors in Ruby's atomic operations headers:

./include/ruby/atomic.h:223:33: error: passing argument 1 of 'rbimpl_atomic_size_exchange' from incompatible pointer type [-Wincompatible-pointer-types]
./include/ruby/atomic.h:237:28: error: passing argument 1 of 'rbimpl_atomic_size_cas' from incompatible pointer type [-Wincompatible-pointer-types]
make: *** [Makefile:468: random.o] Error 1

Context

• The workflow uses fail-fast: false so Unix builds still succeed — this is non-blocking for the primary use case (filling Linux/macOS gaps)
• Windows builds from RubyInstaller are already mirrored via mirror-sync, so the build-from-source Windows path is only needed when RubyInstaller hasn't published a build yet
• There's no known mapping of Ruby version → compatible MinGW/GCC toolchain version
• Pinning a specific toolchain version per Ruby version would be fragile and hard to maintain

Possible approaches

• Pin an older MinGW toolchain version in MSYS2 (need to determine which version per Ruby release)
• Apply source patches to Ruby before building (e.g., fix atomic.h for newer GCC)
• Use RubyInstaller2's build recipes which already handle toolchain compatibility
• Skip Windows in build-from-source entirely since RubyInstaller covers it
• Accept failures as non-blocking (current behavior)

References

• Workflow: .github/workflows/build-ruby-from-source.yml
• Failed run: https://github.com/CodingWithCalvin/dtvem.cli/actions/runs/21842161184/job/63029102987