Quick tip, if you are running the SFDX plugin installation commands in your .yaml scripts docker file image for CI. You would be prompted to confirm. Since this is automated the easiest way to echo the confirmation.

Command:

sfdx plugins:install sfdx-git-delta

Result:

This plugin is not digitally signed and its authenticity cannot be verified. Continue installation y/n?:     

Simply update the script to:

echo 'y' | sfdx plugins:install sfdx-git-delta