Update variants for Nucleo G4 boards

Author: valeros

boards/nucleo_g431rb.json

@@ -6,7 +6,7 @@
     "f_cpu": "170000000L",
     "mcu": "stm32g431rbt6",
     "product_line": "STM32G431xx",
-    "variant": "STM32G4xx/G431R(6-8-B)(I-T)_G441RB(I-T)"
+    "variant": "STM32G4xx/G431R(6-8)(I-T)_G431RB(I-T)x(Z)_G441RB(I-T)"
   },
   "connectivity": [
     "can"

boards/nucleo_g474re.json

@@ -6,7 +6,7 @@
     "f_cpu": "170000000L",
     "mcu": "stm32g474ret6",
     "product_line": "STM32G474xx",
-    "variant": "STM32G4xx/G473R(B-C-E)T_G474R(B-C-E)T_G483RET_G484RET"
+    "variant": "STM32G4xx/G473R(B-C)T_G473RETx(Z)_G474R(B-C-E)T_G483RET_G484RET"
   },
   "connectivity": [
     "can"