CHANGELOG.md: add release heading for v0.57.0

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

Change-Id: I6f550e5b69c7f72f0f9259c8debdacf226947feb
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/801580
Auto-Submit: Gopher Robot <gobot@golang.org>
Reviewed-by: Madeline Kalil <mkalil@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Hongxiang Jiang <hxjiang@golang.org>

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index eec04f8..a886c4a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,15 @@
 
 ## Unreleased
 
+## v0.57.0 (prerelease)
+
+Date: 2026-07-16
+
+This is the [pre-release version](https://code.visualstudio.com/api/working-with-extensions/publishing-extension#prerelease-extensions) of v0.58.
+
+**Full Changelog**: https://github.com/golang/vscode-go/compare/v0.56.0-rc.1...v0.57.0
+**Milestone**: https://github.com/golang/vscode-go/issues?q=milestone%3Av0.58.0
+
 ## v0.56.0
 
 Date: 2026-07-15