fix(DEE-3645): wrap bare TXT in backticks in prose (style guide)

Author: ngayerie

src/content/docs/cloudflare-for-platforms/cloudflare-for-saas/security/certificate-management/issue-and-validate/validate-certificates/troubleshooting.mdx

@@ -75,7 +75,7 @@ Check whether the delegation CNAME is in place at the `_acme-challenge` hostname
 dig _acme-challenge.example.com CNAME +short
 ```
 
-- If this returns **nothing**, the delegation CNAME is missing. Run a TXT query to check whether a hardcoded record is also present:
+- If this returns **nothing**, the delegation CNAME is missing. Run a `TXT` query to check whether a hardcoded record is also present:
 
   ```sh
   dig _acme-challenge.example.com TXT +short