Declare optional package versions

Author: valeros

platform.json

@@ -33,13 +33,15 @@
     "toolchain-gccarmnoneeabi": {
       "type": "toolchain",
       "owner": "platformio",
-      "version": "~1.80201.0"
+      "version": "~1.80201.0",
+      "optionalVersions": ["~1.90201.0"]
     },
     "framework-mbed": {
       "type": "framework",
       "optional": true,
       "owner": "platformio",
-      "version": "~6.60600.0"
+      "version": "~6.60600.0",
+      "optionalVersions": ["~6.51506.0"]
     },
     "framework-zephyr": {
       "type": "framework",