puppet: Increase download timeout from 5m to 10m.

The default timeout for `exec` commands in Puppet is 5 minutes[1].  On
slow connections, this may not be sufficient to download larger
downloads, such as the ~135MB golang tarball.

Increase the timeout to 10 minutes; this is a minimum download speed
of is ~225kB/s.

Fixes #21449.

[1]: https://puppet.com/docs/puppet/5.5/types/exec.html#exec-attribute-timeout

puppet/zulip/manifests/sha256_tarball_to.pp

@@ -11,5 +11,6 @@ define zulip::sha256_tarball_to(
   exec { $url:
     command => "${::zulip_scripts_path}/setup/sha256-tarball-to ${sha256} ${url} ${install_expanded}",
     creates => $a_file,
+    timeout => 600,
   }
 }