Add private location agent v8.3.4 changelog

Author: hwartig

platform/private-locations/change-log.mdx

@@ -16,6 +16,11 @@ Learn more about:
 
 ## Full release history
 
+<Update label="v8.3.4" tags={["June 2026"]}>
+- Update various dependencies to fix vulnerabilities
+- Add `--refresh-cache` functionality
+</Update>
+
 <Update label="v8.3.3" tags={["June 2026"]}>
 - Fixed a bug that caused agent health and readiness probes to fail during graceful shutdown.
 </Update>