cmd/guru: update referrers-json testdata to reflect new line numbering

CL 313251 fixed the describe test, but inadvertently broke the referrers
test due to changing line numbers in describe/main.go. This CL amends
those line numbers.

Fixes golang/go#45778

Change-Id: I1dbdd9157091e061bfa35ec0b5c4690aa09ae092
Reviewed-on: https://go-review.googlesource.com/c/tools/+/313669
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

cmd/guru/testdata/src/referrers-json/main.golden

@@ -43,7 +43,7 @@
 	"package": "describe",
 	"refs": [
 		{
-			"pos": "testdata/src/describe/main.go:92:8",
+			"pos": "testdata/src/describe/main.go:95:8",
 			"text": "\tvar _ lib.Outer // @describe lib-outer \"Outer\""
 		}
 	]