Upgrade @octokit/request.js to v8.1.5 after updating to run on node20

[JamesMGreene]

Upgrading to @octokit/request.js at v8.1.5 will improve the occasional reports we get including invalid json response body in the error output, e.g.:

• Issue deploying github-pages artifact  #146
• Deployment fails if the branchname contains special characters #185
• The user 'System:PublicAccess;aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa' is not authorized to access this resource #236

To be clear, the upgrade will not fix those issues, it will just give us cleaner error message reporting.

The path to this upgrade includes:

• Merge PR Update action to node20 #256
  • Newer Octokit drops support for Node 16.x
• Upgrade to @actions/github@^6.0.0
  • This include a dependency on @octokit/core@^5.0.0
    • This include a dependency on @octokit/request@^8.0.0 with this PR merged
• Release as v3.0.0 (and v3)

The equivalent for v1 and v2 will be:

• Add rough error handler for Octokit response parsing failures to 1.x and 2.x release #265