add type to enums to fix Linter error R3015 (Azure#16775)

Author: stephenbudhi-msft

specification/reservations/resource-manager/Microsoft.Capacity/stable/2020-10-25/quota.json

@@ -748,6 +748,7 @@
         "Failed",
         "InProgress"
       ],
+      "type": "string",
       "x-ms-enum": {
         "name": "QuotaRequestState",
         "modelAsString": true
@@ -762,6 +763,7 @@
         "shared",
         "serviceSpecific"
       ],
+      "type": "string",
       "x-ms-enum": {
         "name": "ResourceType",
         "modelAsString": true