Upgrade GitHub Actions for Node 24 compatibility (#8102)

## Summary

Upgrade GitHub Actions to their latest versions to ensure compatibility
with Node 24, as Node 20 will reach end-of-life in April 2026.

## Changes

| Action | Old Version(s) | New Version | Release | Files |
|--------|---------------|-------------|---------|-------|
| `actions/setup-node` |
[`v5`](https://github.com/actions/setup-node/releases/tag/v5) |
[`v6`](https://github.com/actions/setup-node/releases/tag/v6) |
[Release](https://github.com/actions/setup-node/releases/tag/v6) |
ci.yml, rust-release.yml, sdk.yml, shell-tool-mcp-ci.yml,
shell-tool-mcp.yml |

## Context

Per [GitHub's
announcement](https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/),
Node 20 is being deprecated and runners will begin using Node 24 by
default starting March 4th, 2026.

### Why this matters

- **Node 20 EOL**: April 2026
- **Node 24 default**: March 4th, 2026
- **Action**: Update to latest action versions that support Node 24

### Security Note

Actions that were previously pinned to commit SHAs remain pinned to SHAs
(updated to the latest release SHA) to maintain the security benefits of
immutable references.

### Testing

These changes only affect CI/CD workflow configurations and should not
impact application functionality. The workflows should be tested by
running them on a branch before merging.

.github/workflows/shell-tool-mcp-ci.yml

@@ -30,7 +30,7 @@ jobs:
           run_install: false
 
       - name: Setup Node.js
-        uses: actions/setup-node@v5
+        uses: actions/setup-node@v6
         with:
           node-version: ${{ env.NODE_VERSION }}
           cache: "pnpm"