fetch-contributor-data: Modernize set literal syntax.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

tools/fetch-contributor-data

@@ -71,14 +71,12 @@ def fetch_contributors(repo_name: str, max_retries: int) -> List[Contributor]:
     retry = Retry(
         total=max_retries,
         backoff_factor=2.0,
-        status_forcelist=set(
-            [
+        status_forcelist={
             403,  # Github does unauth rate-limiting via 403's
             429,  # The formal rate-limiting response code
             502,  # Bad gateway
             503,  # Service unavailable
-            ]
-        ),
+        },
     )
     session = GithubSession(max_retries=retry)
     while True: