Report submodule status when not valid work-tree

[zvecr]

Description

[zvecr@zvecr-zen qmk_firmware-master]$ qmk doctor
...
⚠ QMK home does not appear to be a Git repository! (no .git folder)
...
Ψ Submodules are up to date.
Ψ Submodule status:
Ψ QMK is ready to go, but minor problems were found

Slightly misleading saying everything is ready...

Now the output is,

[zvecr@zvecr-zen qmk_firmware-master]$ qmk doctor
...
⚠ QMK home does not appear to be a Git repository! (no .git folder)
...
Ψ Submodule status:
☒ - lib/chibios: <<< missing or unknown >>>
☒ - lib/chibios-contrib: <<< missing or unknown >>>
☒ - lib/googletest: <<< missing or unknown >>>
☒ - lib/lufa: <<< missing or unknown >>>
☒ - lib/vusb: <<< missing or unknown >>>
☒ - lib/printf: <<< missing or unknown >>>
☒ - lib/pico-sdk: <<< missing or unknown >>>
Ψ Major problems detected, please fix these problems before proceeding.
Ψ Check out the FAQ (https://docs.qmk.fm/#/faq_build) or join the QMK Discord (https://discord.gg/Uq7gcHh) for help.

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).