marketplacenotifications: fixing an invalid operation id (#16326)

Since both of these share the same operation id - neither is currently valid / can work
as such this fixes these to use the canonical name (List and Get) based on the convention

Author: tombuildsstuff

specification/marketplacenotifications/resource-manager/Microsoft.MarketplaceNotifications/stable/2021-03-03/MarketplaceNotifications.json

@@ -21,7 +21,7 @@
         "tags": [
           "Notification"
         ],
-        "operationId": "Notifications_GetWithAuthorization",
+        "operationId": "Notifications_List",
         "parameters": [
           {
             "$ref": "#/parameters/SubscriptionId"
@@ -62,7 +62,7 @@
         "tags": [
           "Notification"
         ],
-        "operationId": "Notification_GetWithAuthorization",
+        "operationId": "Notification_Get",
         "parameters": [
           {
             "$ref": "#/parameters/SubscriptionId"