Add consistency to code block language

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: RossTarrant

docs/installation-guides/install-codex.md

@@ -20,7 +20,7 @@ bearer_token_env_var = "GITHUB_PAT_TOKEN"
 
 You can also add it via the Codex CLI:
 
-```cli
+```bash
 codex mcp add github --url https://api.githubcopilot.com/mcp/ --bearer-token-env-var GITHUB_PAT_TOKEN
 ```