Improve pyright verification of third-party test cases in CI (#9650)

Co-authored-by: Avasam <samuel.06@hotmail.com>

pyrightconfig.json

@@ -5,6 +5,10 @@
         "stdlib",
         "stubs",
     ],
+    "exclude": [
+        // test cases use a custom config file
+        "stubs/**/@tests/test_cases"
+    ],
     "typeCheckingMode": "basic",
     "strictListInference": true,
     "strictDictionaryInference": true,