Update SDK to latest stable - 6.0.301

It includes fixes for subtype matching as well as `function` matching fix with explicit type abbreviation.

cc @KevinRansom @baronfel @auduchinok

global.json

 {
   "sdk": {
-    "version": "6.0.200",
+    "version": "6.0.301",
     "allowPrerelease": true,
     "rollForward": "minor"
   },
   "tools": {
-    "dotnet": "6.0.200",
+    "dotnet": "6.0.301",
     "vs": {
       "version": "16.8",
       "components": [