cmd/worker: extend redis cache write timeout

Double the timeout for writing to the redis cache instance, from 3 to 6 seconds.

We saw an error on /clear-cache that was due to hitting the write timeout:
https://pantheon.corp.google.com/errors/COmQ7oS0hITl3gE?time=P30D&project=go-discovery
https://pantheon.corp.google.com/logs/query;query=resource.type%3D%22gae_app%22%20resource.labels.module_id%3D%22etl%22%0A%0Atrace%3D%22d3d2cbb054cf3b8e4627e049d3c5cc9e%2F8803268222527035810%3Bo%3D1%22;timeRange=2020-10-12T17:57:33.989Z%2F2020-10-13T12:57:33.989Z?project=go-discovery

Change-Id: Ib9aae6ccece58ecccf78b2627c65a176295199ee
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/261817
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>
diff --git a/cmd/worker/main.go b/cmd/worker/main.go
index f914f79..540dc37 100644
--- a/cmd/worker/main.go
+++ b/cmd/worker/main.go
@@ -171,7 +171,7 @@
 }
 
 func getCacheRedis(ctx context.Context, cfg *config.Config) *redis.Client {
-	return getRedis(ctx, cfg.RedisCacheHost, cfg.RedisCachePort, 0, 0)
+	return getRedis(ctx, cfg.RedisCacheHost, cfg.RedisCachePort, 0, 6*time.Second)
 }
 
 func getRedis(ctx context.Context, host, port string, writeTimeout, readTimeout time.Duration) *redis.Client {