doc: fix certificate display in tls doc

In one context, `<Buffer>` was being interpretted as an HTML tag and not
displayed.

PR-URL: nodejs#35032
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/tls.md

@@ -1065,7 +1065,8 @@ For EC keys, the following properties may be defined:
 
 Example certificate:
 
-```text
+<!-- eslint-skip -->
+```js
 { subject:
    { OU: [ 'Domain Control Validated', 'PositiveSSL Wildcard' ],
      CN: '*.nodejs.org' },