internal/lsp/debug: update hard-coded version for v0.9.0-pre.1

Note while we normally set the version to the final version (v0.9.0), we
are anticipating multiple prereleases and so include the prerelease
label to help differentiate them.

For golang/go#53412

Change-Id: I4e01c80ca2edbd18125c8c64d6a697c08cfcf62c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/412816
gopls-CI: kokoro <noreply+kokoro@google.com>
Run-TryBot: Dylan Le <dungtuanle@google.com>
Reviewed-by: Nooras Saba‎ <saba@golang.org>

internal/lsp/debug/info.go

@@ -29,7 +29,7 @@ const (
 )
 
 // Version is a manually-updated mechanism for tracking versions.
-const Version = "master"
+const Version = "v0.9.0-pre.1"
 
 // 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.