Increase presence ratelimit for tests

This ratelimit is introduced in
element-hq/synapse#18000
and causes some existing Sytests to fail.

Increase the ratelimit in Sytest's Synapse config
so tests pass again.

lib/SyTest/Homeserver/Synapse.pm

@@ -229,6 +229,13 @@ sub start
            },
         },
 
+        rc_presence => {
+           per_user => {
+              per_second => 1000,
+              burst_count => 1000,
+           }
+        }
+
         enable_registration => "true",
         enable_registration_without_verification => "true",
         databases => \%db_configs,