internal/worker: fix unprocessed-modules aggregation

The Count aggregation is the number of data points recorded. We
want the actual value.

Change-Id: I1141c731d1fef105cee9628e7b718a5f3573adde
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/323329
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>

internal/worker/metrics.go

@@ -53,7 +53,7 @@ var (
 	UnprocessedModules = &view.View{
 		Name:        "go-discovery/unprocessed_modules/count",
 		Measure:     unprocessedModules,
-		Aggregation: view.Count(),
+		Aggregation: view.LastValue(),
 		Description: "number of unprocessed modules",
 	}
 )