fix: handle 204 No Content without JSON parsing in http-client.ejs

[SURTBLAZE]

This ensures Hasura correctly handles "No Content" responses without attempting JSON parsing.

Impact on existing features

No breaking changes.
No changes to golden files , code generation output is structurally identical.

Related Issue

Fixes: hasura/graphql-engine#10792

Questions

1. Do you prefer leaving the existing golden tests as are, or should I update / extend golden tests to explicitly assert 204 handling in the HTTP client layer?
2. After merging this fix, I plan to add runtime tests to the main Hasura project (graphql-engine) to ensure correct behavior end-to-end when calling REST APIs that return 204 No Content. Please confirm that this is the preferred place for such tests (as opposed to keeping runtime tests in ndc-open-api-lambda).