Temporarily use ruby_4_0 branch for cross-compile testing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hsbt

.github/workflows/crosscompile.yml

@@ -58,11 +58,20 @@ jobs:
           sparse-checkout: /.github
           persist-credentials: false
 
+      # Temporarily checkout ruby_4_0 to verify cross-compile on a branch that supports it
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          repository: ruby/ruby
+          ref: ruby_4_0
+          path: src
+          persist-credentials: false
+
       - uses: ./.github/actions/setup/directories
         with:
           srcdir: src
           builddir: build
           makeup: true
+          checkout: ''
 
       - name: Install cross-compilation toolchain
         run: |