gopls/internal/lsp/debug: update hard-coded version for v0.12.0

Updates golang/go#59818

Change-Id: I7b17206c97a62a69d045c1067e26b25aa5ecf76c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/488355
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>

gopls/internal/lsp/debug/info.go

diff --git a/gopls/internal/lsp/debug/info.go b/gopls/internal/lsp/debug/info.go
index 00752e6..34fe216 100644
--- a/gopls/internal/lsp/debug/info.go
+++ b/gopls/internal/lsp/debug/info.go
@@ -29,7 +29,7 @@
 )
 
 // Version is a manually-updated mechanism for tracking versions.
-const Version = "master"
+const Version = "v0.12.0"
 
 // ServerVersion is the format used by gopls to report its version to the
 // client. This format is structured so that the client can parse it easily.