fix(anthropic): ignore LangSmith requests in VCR cassettes (#38547)

Anthropic integration tests can run with LangSmith tracing enabled in
scheduled CI, which sends LangSmith API requests while VCR cassettes are
active. Ignore LangSmith ingest endpoints in the Anthropic VCR config so
cassette playback only matches Anthropic traffic.

## Changes
- Add `api.smith.langchain.com` to the Anthropic VCR `ignore_hosts`
configuration while preserving any hosts from the shared base config.
- Keep existing Anthropic cassette serialization, request redaction, and
response redaction behavior unchanged.

libs/partners/anthropic/tests/conftest.py

@@ -25,6 +25,10 @@ def vcr_config() -> dict:
     config["before_record_response"] = remove_response_headers
     config["serializer"] = "yaml.gz"
     config["path_transformer"] = VCR.ensure_suffix(".yaml.gz")
+    config["ignore_hosts"] = [
+        *config.get("ignore_hosts", []),
+        "api.smith.langchain.com",
+    ]
 
     return config