Fixes on the script "Fetch Mac Installer Distribution certificates" of the macOS example project

[daniel-dosiper]

Describe the sample projects update you'd like to see
Fixes on the script "Fetch Mac Installer Distribution certificates" of the macOS example project: https://github.com/codemagic-ci-cd/codemagic-sample-projects/tree/main/flutter/flutter-macos-demo-project

Additional context
The next script of this codemagic.yaml file is not working:

      - name: Fetch Mac Installer Distribution certificates
        script: |
          # HINT: We can use MAC_APP_DISTRIBUTION if looking to package the artifact before submitting it to App Store. 
          # And please note that the certificate type must match the one we are using in the Package macOS application script down below.
          app-store-connect certificates list --type MAC_INSTALLER_DISTRIBUTION --save || \
          app-store-connect certificates create --type MAC_INSTALLER_DISTRIBUTION --save          

The OR combination doesn't work as expected. Although the certificate doesn't exist (the first time the build is launched), the second command with the "create" option is never executed. Both commands work one by one (first launch with "create" and after that "list" to get the certificate).