[ReleasePR billing] Fixing s360 swagger correctness (#1832)

Create to sync Azure/azure-rest-api-specs#15421
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...AzureSDKAutomation:sdkAuto/billing?expand=1)

Author: msftbot[bot]

schemas/2020-05-01/Microsoft.Billing.json

@@ -599,6 +599,21 @@
             }
           ],
           "description": "Dictionary of metadata associated with the invoice section."
+        },
+        "tags": {
+          "oneOf": [
+            {
+              "type": "object",
+              "additionalProperties": {
+                "type": "string"
+              },
+              "properties": {}
+            },
+            {
+              "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
+            }
+          ],
+          "description": "Dictionary of metadata associated with the invoice section. Maximum key/value length supported of 256 characters. Keys/value should not empty value nor null. Keys can not contain < > % & \\ ? /"
         }
       },
       "description": "The properties of an invoice section."