GPU statusbar item uses only the first found GPU rather than select actively used one

[Tbusk]

What Happened?

When running a stress test and looking at GPU usage values, I found that while other areas show lots of GPU usage, the statusbar remained unchanged at 0%.

Looking into this, the issue is that the serialize method in Resources.vala only selects the first found gpu rather than looks for the more active one.

I noticed that it was using the correct percentage values read from the files, but the first gpu had 0 while my active gpu had the correct percentage.

Steps to Reproduce

1. Use a machine with more than one GPU (onboard + graphics card) and have the default one be the one you do not use (e.g., onboard)
2. Use some GPU

Expected Behavior

The status bar either will show percentage for each gpu or show only the most active one.

OS Version

8.x (Circe)

OS Architecture

amd64 (on most hardwares)

Session Type

Secure Session (Wayland)

Software Version

Compiled from git

Log Output

Hardware Info

No response