Scan for security vulnerabilities with GitHub CodeQL by adding .github/workflows/codeql.yml workflow.

Use CodeQL for as much as possible:

• Available languages:
  • swift
  • actions (GitHub Workflows)
• Search for other languages:
  • zsh
  • YAML besides GitHub Workflows
  • JSON (+ Package.resolved, .swift-format)
  • Markdown

Also ensure dependabot is setup properly:

https://docs.github.com/en/code-security/getting-started/dependabot-quickstart-guide