Portasol plays regular Umbrella SFX when raining in Caves

It's because caveweather.lua doesn't account for it, weather.lua does. That said, the umbrella rain sound has a unique version for the caves, so I don't know if they'd also want to make a unique version of it for the portasol too, or the existing alternative one used in the surface would suffice, I haven't listened to it to know.

Changed Status to Fixed

I've hooked up the metallic rain sound. We may make a unique sound for it later, to match the lower levels of rain in the caves.