Fixes issue

There's a typo in the CLI.

Describe the change

Fixes the command to use the correct double dash for the long parameter.

How to verify it

Changelog text

• Fix: Fix the cosign use-signing-config flag.

Please verify and check that the pull request fulfills the following requirements

• Tests have been added or not applicable
• Documentation updates are included or not applicable (most documentation should be in the regclient.org repo)
• Changes have been rebased to main
• Multiple commits to the same code have been squashed
• All changes have been human generated or created with a reproducible tool