CHANGELOG.md: update v0.22.1 release date

It was delayed due to last minute CI issues

Change-Id: If2e801b9c849f1df70349f70b30dfd98af257c64
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/290391


Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>