internal/jobs: increase firestore retries

Increase by 5x the number of times the Firestore client will retry when there
is a transaction conflict.

We hope this will resolve the errors we see in the worker logs.

Change-Id: I65f2c69746f04165b9f7eed9572d428e8186801f
Reviewed-on: https://go-review.googlesource.com/c/pkgsite-metrics/+/499600
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Zvonimir Pavlinovic <zpavlinovic@google.com>
diff --git a/internal/jobs/firestore.go b/internal/jobs/firestore.go
index 859c154..6f6a2bc 100644
--- a/internal/jobs/firestore.go
+++ b/internal/jobs/firestore.go
@@ -88,7 +88,8 @@
 			return err
 		}
 		return tx.Set(docref, j)
-	})
+	},
+		firestore.MaxAttempts(firestore.DefaultTransactionMaxAttempts*5))
 }
 
 // ListJobs calls f on each job in the DB, most recently started first.