ci(backport): Update GitHub Actions

[matthewfeickert]

Description

• Backport:
  • PR chore: Install pandoc manually from GitHub release binaries #2307
  • PR build(deps): bump actions/checkout from 3 to 4 #2313

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Backport:
   - PR https://github.com/scikit-hep/pyhf/pull/2307
   - PR https://github.com/scikit-hep/pyhf/pull/2313