ci: request Ruby 4 in cross-gem as semver requirement

Author: kateinoigakukun

.github/workflows/build-gems.yml

@@ -50,7 +50,7 @@ jobs:
         id: cross-gem
         with:
           platform: ${{ matrix.ruby-platform }}
-          ruby-versions: ${{ join(fromJSON(needs.ci-data.outputs.result).stable-ruby-versions, ',') }}
+          ruby-versions: ${{ replace(join(fromJSON(needs.ci-data.outputs.result).stable-ruby-versions, ','), '4.0', '~> 4.0.0') }}
 
       - uses: actions/upload-artifact@v7
         with: