internal/worker: log some InsertModule errors at Info

If the error's status is less than 500, log as Info rather than Error.

Change-Id: Id8cfeceac4063f77a3461f3c27786f34424c920e
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/349754
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>

internal/worker/fetch.go

diff --git a/internal/worker/fetch.go b/internal/worker/fetch.go
index a6aa35e..a2fb408 100644
--- a/internal/worker/fetch.go
+++ b/internal/worker/fetch.go
@@ -362,10 +362,13 @@
 	isLatest, err := f.DB.InsertModule(ctx, ft.Module, lmv)
 	ft.timings["db.InsertModule"] = time.Since(start)
 	if err != nil {
-		log.Error(ctx, err)
-
 		ft.Status = derrors.ToStatus(err)
 		ft.Error = err
+		if ft.Status >= 500 {
+			log.Error(ctx, err)
+		} else {
+			log.Info(ctx, err)
+		}
 		return ft
 	}
 	log.Debugf(ctx, "db.InsertModule succeeded for %s@%s", ft.ModulePath, ft.RequestedVersion)