Changed modelAsString for SecurityType param in Microsoft.Compute spec to true (Azure#14640)

Author: ms-saypaul

specification/compute/resource-manager/Microsoft.Compute/stable/2020-12-01/compute.json

@@ -9186,7 +9186,7 @@
           ],
           "x-ms-enum": {
             "name": "SecurityTypes",
-            "modelAsString": false
+            "modelAsString": true
           }
         }
       },

specification/compute/resource-manager/Microsoft.Compute/stable/2021-03-01/compute.json

@@ -10019,7 +10019,7 @@
           ],
           "x-ms-enum": {
             "name": "SecurityTypes",
-            "modelAsString": false
+            "modelAsString": true
           }
         }
       },