Describe the problem

Machine-readable formatting produces text output.

To reproduce

$ arduino-cli core update-index --format yaml
Downloading index: package_index.tar.bz2 downloaded                                                                                 
Downloading index: package_esp8266com_index.json downloaded       
$

Expected behavior

$ arduino-cli core update-index --format yaml
$

Arduino CLI version

nightly

Operating system

N/A

Operating system version

all

Additional context

No response

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the nightly build
• My report contains all necessary details