Upgrade `github/codeql` dependency to 2.18.4

[github-actions[bot]]

This PR upgrades the CodeQL CLI version to 2.18.4.

CodeQL dependency upgrade checklist:

• [ ] Confirm the code has been correctly reformatted according to the new CodeQL CLI.
• [ ] Identify any CodeQL compiler warnings and errors, and update queries as required.
• [ ] Validate that the github/codeql test cases succeed.
• [ ] Address any CodeQL test failures in the github/codeql-coding-standards repository.
• [ ] Validate performance vs pre-upgrade, using /test-performance