extension/CHANGELOG.md: add v0.40.2 entry

For #3142

Change-Id: I71ef7ed943472f4e5f9b979c9f077c3f959eaaa7
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/556858
Commit-Queue: Hyang-Ah Hana Kim <[email protected]>
TryBot-Result: kokoro <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: hyangah

extension/CHANGELOG.md

@@ -1,3 +1,8 @@
+## v0.40.2 - 22 Jan, 2023
+
+This is a point release to update the upcoming developer survey information
+([the commit history](https://github.com/golang/vscode-go/compare/v0.40.1...v0.40.2)).
+
 ## v0.40.1 - 21 Dec, 2023
 
 This is a point release to fix minor bugs. A comprehensive list of bug fixes and