Do not download slow test when on sandcastle (#57953)

Summary:
Downloading slow_test list on SC causes timeout, this is even a bigger issue since `common_utils.py` is reused in many internal projects/modules.

Pull Request resolved: #57953

Test Plan: CI

Reviewed By: janeyx99

Differential Revision: D28325527

fbshipit-source-id: ae47c9e43ad6f416008005bb26ceb2f3d6966f2e

torch/testing/_internal/common_utils.py

@@ -856,8 +856,11 @@ def is_cached_file_valid():
 def check_slow_test_from_stats(test):
     global slow_tests_dict
     if slow_tests_dict is None:
-        url = "https://raw.githubusercontent.com/pytorch/test-infra/master/stats/slow-tests.json"
-        slow_tests_dict = fetch_and_cache(".pytorch-slow-tests", url)
+        if not IS_SANDCASTLE and os.getenv("PYTORCH_RUN_DISABLED_TESTS", "0") != "1":
+            url = "https://raw.githubusercontent.com/pytorch/test-infra/master/stats/slow-tests.json"
+            slow_tests_dict = fetch_and_cache(".pytorch-slow-tests", url)
+        else:
+            slow_tests_dict = {}
     test_suite = str(test.__class__).split('\'')[1]
     test_name = f'{test._testMethodName} ({test_suite})'