test2405: report `fd_count*` variables on failure

test2405: report `fd_count*` variables on failure

This test is frequently failing in macOS !ssl jobs:

"curl_multi_waitfds() should return at least the number of fds needed":
https://github.com/curl/curl/actions/runs/19290229745/job/55159015942 AM clang !ssl !debug brotli zstd
https://github.com/curl/curl/actions/runs/19289578332/job/55157058146 AM clang !ssl !debug brotli zstd
https://github.com/curl/curl/actions/runs/19188515879/job/54859474947 AM clang !ssl
https://github.com/curl/curl/actions/runs/19165077858/job/54783776869 AM clang !ssl libssh2 AppleIDN
https://github.com/curl/curl/actions/runs/19046554157/job/54396096298 AM gcc-12 !ssl !debug

"curl_multi_waitfds() should return the amount of fds needed if enough isn't passed in":
https://github.com/curl/curl/actions/runs/19184546172/job/54848549080 AM gcc-13 !ssl !debug

Also high on the test clutch list:
2405 FAIL times: 165
Ref: https://testclutch.curl.se/static/reports/results-count.html

```
libtests returned 44, when expecting 0

FAIL 2405: 'checking curl_multi_waitfds functionality' multi, HTTP, HTTP/2
```
44 = `CURLE_OBSOLETE44` = `TEST_ERR_FAILURE`

Also: fix a newline in log output.

Follow-up to c78044c07e97cb720049579f4fe3cab33a7ea8d3 #15146 #15155

Closes #19481