docs: add changes block for tls.getCACertificates ‘as’ option support

Author: haramj

doc/api/tls.md

@@ -2314,6 +2314,9 @@ tls.setDefaultCACertificates([...currentCerts, ...additionalCerts]);
 added:
   - v23.10.0
   - v22.15.0
+changes:
+  - Added support for the `as` option to specify the return format of certificates (`buffer` or `x509`).
+  - Updated the default return format to be `buffer`.
 -->
 
 * `options` {string|Object|undefined}