smarthttp_test: satisfy errcheck + revive on new tests

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nodo5mo ago

golangci-lint v2.11.4 (matches CI) flagged the discarded w.Write returns and unused *http.Request parameter in the two new FollowInfoRefsRedirect tests.

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com Entire-Checkpoint: 0b59e56d2ab4