Update mbed package to the latest v6.8.0

Author: valeros

platform.json

@@ -84,7 +84,7 @@
       "type": "framework",
       "optional": true,
       "owner": "platformio",
-      "version": "~6.60600.0",
+      "version": "~6.60800.0",
       "optionalVersions": [
         "~6.51506.0"
       ]