CHANGELOG.md: add release heading for v0.52.1

This is an automated CL which updates the CHANGELOG.md.

Change-Id: If8f78cda19b6fedf637a95a56e0281c0a0bab17b
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/731121
Commit-Queue: Gopher Robot <gobot@golang.org>
Reviewed-by: Peter Weinberger <pjw@google.com>
TryBot-Bypass: Madeline Kalil <mkalil@google.com>
Auto-Submit: Gopher Robot <gobot@golang.org>
Reviewed-by: Madeline Kalil <mkalil@google.com>

Author: gopherbot

CHANGELOG.md

@@ -5,6 +5,13 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/).
 
 ## Unreleased
 
+## v0.52.1
+
+Date: 2025-12-18
+
+**Full Changelog**: https://github.com/golang/vscode-go/compare/v0.52.0...v0.52.1
+**Milestone**: https://github.com/golang/vscode-go/issues?q=milestone%3Av0.52.1
+
 ## v0.52.0
 
 Date: 2025-12-17