Fix add x-ms-enum (Azure#18406)

* Fix add x-ms-enum

* Fix unrelated test add required type

Author: Frey-Wang

specification/datafactory/resource-manager/Microsoft.DataFactory/stable/2018-06-01/datafactory.json

@@ -6756,7 +6756,11 @@
           "description": "Data flow reference type.",
           "enum": [
             "DataFlowReference"
-          ]
+          ],
+          "x-ms-enum": {
+            "name": "DataFlowReferenceType",
+            "modelAsString": true
+          }
         },
         "referenceName": {
           "type": "string",
@@ -6844,7 +6848,11 @@
           "description": "Managed Virtual Network reference type.",
           "enum": [
             "ManagedVirtualNetworkReference"
-          ]
+          ],
+          "x-ms-enum": {
+            "name": "ManagedVirtualNetworkReferenceType",
+            "modelAsString": true
+          }
         },
         "referenceName": {
           "type": "string",
@@ -7043,7 +7051,11 @@
           "description": "Credential reference type.",
           "enum": [
             "CredentialReference"
-          ]
+          ],
+          "x-ms-enum": {
+            "name": "CredentialReferenceType",
+            "modelAsString": true
+          }
         },
         "referenceName": {
           "type": "string",

specification/datafactory/resource-manager/Microsoft.DataFactory/stable/2018-06-01/entityTypes/Trigger.json

@@ -510,7 +510,11 @@
           "type": "string",
           "enum": [
             "TriggerReference"
-          ]
+          ],
+          "x-ms-enum": {
+            "name": "TriggerReferenceType",
+            "modelAsString": true
+          }
         },
         "referenceName": {
           "description": "Reference trigger name.",