fix(ci): specify toolchain version in release workflow

[zouguangxian]

Summary

• Add explicit toolchain: stable parameter to rust-toolchain GitHub Action in release workflow
• Ensures consistent Rust version during automated release process

Changes

• Updated .github/workflows/release.yml to specify toolchain version explicitly
• Prevents potential issues from implicit toolchain selection

Test plan

• Verify workflow YAML syntax is valid
• Monitor next release workflow execution to confirm stable toolchain usage

🤖 Generated with Claude Code

[cursor]

PR Summary

Low Risk
Small CI-only change that just makes the release workflow’s Rust toolchain selection explicit.

Overview
Pins the release workflow’s Rust setup step to an explicit toolchain: stable when installing via dtolnay/rust-toolchain, reducing ambiguity in the toolchain chosen during automated releases.

^{Written by Cursor Bugbot for commit eb33e17. This will update automatically on new commits. Configure here.}