fix: adjust release commit message to messageonly on sec release

Fixes: nodejs-private/security-release#48

Author: RafaelGSS

lib/prepare_release.js

@@ -622,7 +622,7 @@ export default class ReleasePreparation extends Session {
 
     const notableChanges = await this.getBranchDiff({
       onlyNotableChanges: true,
-      format: 'plaintext'
+      format: isSecurityRelease ? 'messageonly' : 'plaintext'
     });
     messageBody.push('Notable changes:\n\n');
     if (isLTSTransition) {