fix(checkver): Correct error messages

[lewis-yeung]

Description

When checking update and the $script is used, an error message should mention the output of script instead of $url.

Checklist:

• [x] I have read the Contributing Guide.
• [x] I have ensured that I am targeting the develop branch.
• [ ] I have updated the documentation accordingly.
• [ ] I have updated the tests accordingly.
• [x] I have added an entry in the CHANGELOG.