chore(ci): upgrade Node.js version from 16 to 20 in workflows

[angelcaamal]

Description

• Upgrades Node.js runtime target from 16 to 20 in CI test workflow configurations (.github/workflows/test-sample.yml).
• Fixes zizmor/template-injection security warnings by routing workflow inputs (name and path) through intermediate environment variables before executing shell commands.

Fixes Internal: b/553550396

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• Required CI tests pass (see CI testing)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

Note: Any check with (dev), (experimental), or (legacy) can be ignored and should not block your PR from merging (see CI testing).

[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.

[Kef131]

As mentioned in the description, the CI is throwing errors until Node20 is merged on this PR