remote-blackbox: Increase scrape timeout

In order to avoid false positives, especially with Invoice Ninja, I'm
increasing the timeout values for scraping the public-facing websites.
They can occasionally be quite slow, either because of our Internet
connection, or load on the servers.

group_vars/remote-blackbox.yml

@@ -16,7 +16,6 @@ blackbox_modules:
       - 307
       - 308
     prober: http
-    timeout: 5s
 
 vmagent_remotewrite_url: https://metrics.pyrocufflink.blue/insert/1/prometheus/api/v1/write
 
@@ -33,6 +32,7 @@ vmagent_scrape_configs:
 
 - job_name: websites
   scrape_interval: 4m
+  scrape_timeout: 30s
   metrics_path: /probe
   params:
     module: