config: temporarily allow 'devel' go version

Many Go team members testing telemetry use gopls built with the go
built from tip.

Updates golang/go#62271

Change-Id: I892b052a599a6f72911c56ddd534572c6086dab7
Reviewed-on: https://go-review.googlesource.com/c/telemetry/+/534476
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Peter Weinberger <[email protected]>

Author: hyangah

config/config.json

@@ -312,7 +312,8 @@
 		"go1.21.0",
 		"go1.21.1",
 		"go1.21.2",
-		"go1.21.3"
+		"go1.21.3",
+		"devel"
 	],
 	"Programs": [
 		{