fix pii entity categories (#13122)

Author: iscai-msft

specification/cognitiveservices/data-plane/TextAnalytics/preview/v3.1-preview.4/TextAnalytics.json

@@ -866,7 +866,7 @@
               "default": "latest",
               "type": "string"
             },
-            "piiCategories": {
+            "pii-categories": {
               "$ref": "#/definitions/PiiCategories"
             },
             "stringIndexType": {