Fixes https://github.com/matrix-org/synapse/issues/10030.

We were expecting milliseconds where we should have provided a value in seconds.

The impact of this bug isn't too bad. The code is intended to count the number of remote servers that the homeserver can see and report that as a metric. This metric is supposed to run initially 1 second after server startup, and every 60s as well. Instead, it ran 1,000 seconds after server startup, and every 60s after startup.

This fix allows for the correct metrics to be collected immediately, as well as preventing a random collection 1,000s in the future after startup.