Build warning when not valid work-tree

[zvecr]

Description

When trying to build via zip, the usual error is ⚠ "git describe --abbrev=6 --dirty --always --tags" returned error code 128 which isnt the most descriptive. This updates to produce the following:

$ make clean kprepublic/jj4x4:default
Deleting .build/ ... done.
WARNING: Target folder is not a git repo.
 Please consider following https://docs.qmk.fm/#/newbs_getting_started.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).