fix: write download result to stderr for docker-compose and mutagen [skip ci]

[stasadev]

The Issue

• feat: add testing for DDEV HEAD github-action-setup-ddev#57

The output has {"level":"info","msg":"Download complete.","time":"2025-11-04T15:37:53+02:00"}, which can break ddev describe -j:

$ rm -f .ddev/.ddev-docker-compose-full.yaml ~/.ddev/bin/docker-compose
$ ddev describe -j 2>/dev/null
{"level":"info","msg":"Download complete.","time":"2025-11-04T15:37:53+02:00"}
{"level":"info","msg":"┌────────────────────────────────────────────────────────────────────────────────────┐\n│ Project..."}

This happened after this change:

• fix(describe): show service info when project is stopped, fixes #7159 #7768

How This PR Solves The Issue

Moves Download complete. to stderr.

Manual Testing Instructions

rm -f .ddev/.ddev-docker-compose-full.yaml ~/.ddev/bin/docker-compose
ddev describe -j 2>/dev/null

Automated Testing Overview

Release/Deployment Notes