docs: add cache lock language key changelog

Signed-off-by: memleakd <121398829+memleakd@users.noreply.github.com>

Author: memleakd

user_guide_src/source/changelogs/v4.8.0.rst

@@ -274,6 +274,9 @@ Others
 Message Changes
 ***************
 
+- Added new language key:
+    - ``Cache.unsupportedLockStore`` (``CacheException::forUnsupportedLockStore()``)
+
 - Removed deprecated language keys tied to removed exception constructors:
     - ``Core.missingExtension`` (``FrameworkException::forMissingExtension()``)
     - ``HTTP.cannotSetCache`` (``DownloadException::forCannotSetCache()``)