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

We typically set the hard-coded version to the release version, even for
prereleases (else we can't tag a final release that is the same ref as
the prerelease).

For golang/go#53412

Change-Id: I57323d6a082e8fc410e4d0c8e8af7c61d13e65d9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/414497
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Findley <rfindley@google.com>

internal/lsp/debug/info.go

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