What happened in your environment?

If oras manifest fetch is used with --pretty set and --output set to a file, then the output file is prettified

What did you expect to happen?

According to the help doc, --pretty should only prettify stdout output

--pretty prettify JSON objects printed to stdout

How can we reproduce it?

 oras manifest fetch -o out mcr.microsoft.com/oss/kubernetes/kubectl:v1.31.0-alpha.0 --platform linux/amd64 --pretty

The saved file out will be prettified.

What is the version of your ORAS CLI?

Version: 1.2.0-beta.1+unreleased
Go version: go1.22.1
Git commit: fa65f61
Git tree state: dirty

What is your OS environment?

Ubuntu 20.04

Are you willing to submit PRs to fix it?

• Yes, I am willing to fix it.