completion: fix zsh completion

[chenrui333]

Description

Update zsh completion per spf13/cobra#1690

Also relates to Homebrew/homebrew-core#107394

Motivation and Context

• I have raised an issue to propose this change, which has been given a label of design/approved by a maintainer (required)

How Has This Been Tested?

Are you a GitHub Sponsor yet (Yes/No?)

• Yes
• No

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Documentation

• I have updated the list of tools in README.md if (required) with ./arkade get -o markdown
• I have updated the list of apps in README.md if (required) with ./arkade install --help

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s
• I have added tests to cover my changes.
• All new and existing tests passed.

• I have tested this on arm, or have added code to prevent deployment

[chenrui333]

Actually this is not needed, my bad.