fix: tag regions by the branch the code takes

Mega CD US BIOS serves every non-EU, non-JP disc; Dolphin boots
Korean discs from the JAP directory; Beetle never opens scph5903.bin
under that name.

install/retrodeck.json

@@ -26064,6 +26064,7 @@
         "sega-mega-cd"
       ],
       "regions": [
+        "latin-america",
         "north-america"
       ],
       "region_system_groups": [
@@ -28809,12 +28810,6 @@
       ],
       "systems": [
         "sony-playstation"
-      ],
-      "regions": [
-        "japan"
-      ],
-      "region_groups": [
-        "sony-playstation"
       ]
     },
     {
@@ -76773,7 +76768,8 @@
         "triforce"
       ],
       "regions": [
-        "japan"
+        "japan",
+        "south-korea"
       ],
       "region_groups": [
         "Dolphin:file:GC/JAP/IPL.bin"
@@ -78558,7 +78554,8 @@
         "ishiiruka"
       ],
       "regions": [
-        "japan"
+        "japan",
+        "south-korea"
       ],
       "region_groups": [
         "Ishiiruka:file:dolphin-emu/Sys/GC/JAP/IPL.bin"
@@ -82785,6 +82782,7 @@
         "sega-mega-cd"
       ],
       "regions": [
+        "latin-america",
         "north-america"
       ],
       "region_groups": [
@@ -82805,6 +82803,7 @@
         "sega-mega-cd"
       ],
       "regions": [
+        "latin-america",
         "north-america"
       ],
       "region_groups": [
@@ -82825,6 +82824,7 @@
         "sega-mega-cd"
       ],
       "regions": [
+        "latin-america",
         "north-america"
       ],
       "region_groups": [