Fix global.json. Version ranges are not supported in global.json, also, GitHub actions only supports the latestFeature option (see actions/setup-dotnet#448)

Author: danielcweber

Diff for: global.json

@@ -1,7 +1,7 @@
 {
   "sdk": {
-    "version": "7",
-    "rollForward": "latestMinor",
+    "version": "7.0.0",
+    "rollForward": "latestFeature",
     "allowPrerelease": false
   }
 }