Fix rate_limiter_test.exs test "it restricts based on config values" (#233)

Fix rate_limiter_test.exs test "it restricts based on config values" (#233)

Fixes one of the 'erratic' tests

It used a timer to sleep.
But time also goes on when doing other things, so depending on hardware, the timings could be off.
I slightly changed the tests so we still test what we functionally want.
Instead of waiting until the cache expires I now have a function to expire the test and use that.

That means we're not testing any more if the cache really expires after a certain amount of time,
but that's the responsability of the dependency imo, so shouldn't be a problem.

I also changed `Pleroma.Web.Endpoint, :http, :ip` in the tests to `127.0.0.1`
Currently it was set to 8.8.8.8, but I see no reason for that and, while I assume that no calls
are made to it, it may come over as weird or suspicious to people.

Co-authored-by: Ilja <ilja@ilja.space>
Reviewed-on: https://akkoma.dev/AkkomaGang/akkoma/pulls/233
Co-authored-by: ilja <akkoma.dev@ilja.space>
Co-committed-by: ilja <akkoma.dev@ilja.space>