Add changelog entry

Author: colinrotherham

CHANGELOG.md

@@ -82,6 +82,7 @@ The following functions have been renamed:
 We've made fixes to NHS.UK frontend in the following pull requests:
 
 - [#1301: Support webpack `sass-loader` pkg: scheme with nested paths](https://github.com/nhsuk/nhsuk-frontend/pull/1307)
+- [#1313: Fix header menu margin collapse issue](https://github.com/nhsuk/nhsuk-frontend/pull/1313)
 
 ## 9.5.2 - 14 May 2025