Fix GBA core value (#612)

The current GBA core is loading the `gb` core instead of the `gba`,
preventing GBA games from running.

<img width="1106" height="876" alt="image"
src="https://github.com/user-attachments/assets/5b4569c5-b525-4d70-ade8-928599f55290"
/>
(Screenshot from a GBA game)

This is a simple fix to address this issue.

Author: devdouglasonofre

gaseous-server/Support/PlatformMap.json

@@ -1742,7 +1742,7 @@
           "EmulatorType": "EmulatorJS",
           "AvailableWebEmulatorCores": [
             {
-              "Core": "gb",
+              "Core": "gba",
               "AlternateCoreName": "mgba",
               "Default": true
             }