ci: keep relay checksum awk portable

[ZhiXiao-Lin]

Summary

• preserve the checksum predicate across physical lines with explicit awk continuations
• keep the relay source-verification gate portable to the Ubuntu runner

The first v0.11.1 relay attempt stopped in source verification before its publish step, so no legacy tag, release, or asset was created.

Validation

• executed the exact awk predicate against the public v0.11.1 arm64 macOS checksum
• go run github.com/rhysd/actionlint/cmd/actionlint@v1.7.7 .github/workflows/relay-monorepo-release.yml
• extracted workflow shell programs and validated them with bash -n
• git diff --check