nix path-info: Don't write to std::cout directly (backport #11884)

[mergify[bot]]

Motivation

This interferes with the progress bar, resulting in output like

evaluating derivation 'git+file:///home/eelco/Dev/nix-master#packages.x86_64-linux.default'/nix/store/zz8v96j5md952x0mxfix12xqnvq5qv5x-nix-2.26.0pre20241114_a95f6ea.drv

Context

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This is an automatic backport of pull request #11884 done by Mergify.