doc: update CHANGELOG for upcoming v1.19.1

Author: flavorjones

CHANGELOG.md

@@ -4,6 +4,13 @@ Nokogiri follows [Semantic Versioning](https://semver.org/), please see the [REA
 
 ---
 
+## v1.19.1 / 2026-02-16
+
+### Security
+
+* [CRuby] Address unchecked return value from `xmlC14NExecute` which was a contributing cause to ruby-saml GHSA-x4h9-gwv3-r4m4. See [GHSA-wx95-c6cv-8532](https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-wx95-c6cv-8532) for more information.
+
+
 ## v1.19.0 / 2025-12-28
 
 #### Ruby