`ionic doctor check` attests non-existing "Git doesn't appear to be in use." problem (on Windows)

`ionic doctor check` thinks there is no `git` on my system:

```
PS C:\Projects\Ionic Demo Projects\pwaTest> ionic doctor check
√ Detecting issues: 16 / 16 complete - done!
Detected 3 issues.
[WARN] Git doesn't appear to be in use.

We highly recommend using source control software such as git (https://git-scm.com) to track changes in your code
throughout time. To fix, take the following step(s):

1) Download git if you don't have it installed: https://git-scm.com/downloads
2) Learn the basics if you're unfamiliar with git: https://try.github.io
3) Make your first commit and start tracking code changes! 😍

Ignore this issue with: ionic doctor ignore git-not-used

[WARN] ...

? Fix automatically? No
[WARN] ...

2 issues need to be fixed manually.
```
My system disagrees:
```
PS C:\Projects\Ionic Demo Projects\pwaTest> git status
On branch master
Changes not staged for commit:
(use "git add ..." to update what will be committed)
(use "git checkout -- ..." to discard changes in working directory)

modified: ionic.config.json

no changes added to commit (use "git add" and/or "git commit -a")
```

Start by reproducing `ionic doctor check` on Windows in the reported Git repository, then trace the `git-not-used` diagnostic from the CLI entry point. Compare the diagnostic's repository detection with the reported `git status` result. Done means an active Git repository is no longer reported as unused.

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