Feature: Update gh-pages workflow for faster deployment

[smpark7]

Background and motivation

• GitHub now provides 4 processors instead of 2 for GitHub actions.
• Ubuntu 20.04 will lose support in 2025.

Description of idea

• We can run the make command with 4 threads instead of 2 threads to have gh-pages deploy faster.
• We should also update the Ubuntu OS of the GitHub action to 22.04 or 24.04.
  • Note: This workflow is not a test. Comprehensive OS coverage is not needed.

Implementation details

Edit the make and ubuntu OS lines in .github/workflows/auto-update-gh-pages.yml

Potential snags

Newer Ubuntu OSes may not be compatible with the existing workflows in the gh-pages action.