test(file-logger): cover per-node upstream_unresolved_host mapping

[shreemaan-abhishek]

Description

Follow-up test coverage for upstream_unresolved_host (added in #13568).

The multi-node test added in #13568 (file-logger.t TEST 23/24) uses two identical localhost nodes. That proves the multi-node server_picker branch in apisix/balancer.lua runs, but not that addr_to_domain[server] maps the picked server to its own host, so a wrong-mapping regression could slip through.

Changes

• t/plugin/file-logger.t: add TEST 25/26 using a mixed upstream, one domain node (localhost:1980) and one raw-IP node (127.0.0.1:1982). Round-robin visits both across the request cycle; the test collects the pre-DNS host logged for each resolved upstream and asserts:

  • the domain node logs its hostname (localhost),
  • the raw-IP node falls back to the ip (127.0.0.1).

  This validates the per-server addr_to_domain mapping and the res.domain or res.host fallback. Existing TEST 23/24 are preserved.

Test-only change, no source or schema change.

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change (N/A, test-only)
• I have verified that this change is backward compatible (test-only)