Simplify git command, by letting exceptions go through

[abravalheri]

Purpose

This is an attempt to improve the UX when the git command is not installed.
As we can see in #712, the error might not be very intuitive to understand.

Approach

In this PR I am tried to simplify the code paths and let the shell exception happen.
(After looking at the commit history for the file I can see that we encountered in the past a lot of problems and with the we accumulated very sophisticated checks. It seems to me that we no longer need to return None in pyscaffold.shell.get_git_cmd, because now it will be executed lazily and therefore wait until the logging is properly configured).

[coveralls]

Coverage: 97.919% (+0.07%) from 97.847% when pulling 2d0a40c on issue-712 into 83c7d5d on master.

[abravalheri]

I tested this manually using a windows container:

> docker run --rm -it python:3.10-windowsservercore-1809 powershell

cd $env:TEMP
Invoke-WebRequest -Uri https://github.com/pyscaffold/pyscaffold/archive/refs/heads/issue-712.zip -OutFile pyscaffold.zip
Expand-Archive -LiteralPath pyscaffold.zip -DestinationPath .
# Workaround for setuptools-scm
new-item pyscaffold-issue-712/.git_archival.txt
@"
node: 8c11fff53f49bd616bec72586e6e93ddb0c9c119
node-date: 2023-04-14T11:35:56+01:00
describe-name: v4.4.1b
ref-names: HEAD -> issue-712, origin/issue-712
"@ | add-content -Path pyscaffold-issue-712/.git_archival.txt
python -m pip install ./pyscaffold-issue-712
python -m pyscaffold.cli myproj
# Traceback (most recent call last):
#   File "C:\Python\lib\runpy.py", line 196, in _run_module_as_main
#     return _run_code(code, main_globals, None,
#   File "C:\Python\lib\runpy.py", line 86, in _run_code
#     exec(code, run_globals)
#   File "C:\Python\lib\site-packages\pyscaffold\cli.py", line 267, in <module>
#     main(sys.argv[1:])
#   File "C:\Python\lib\site-packages\pyscaffold\cli.py", line 256, in main
#     opts["command"](opts)
#   File "C:\Python\lib\site-packages\pyscaffold\cli.py", line 225, in run_scaffold
#     api.create_project(opts)
#   File "C:\Python\lib\site-packages\pyscaffold\api.py", line 156, in create_project
#     return reduce(actions.invoke, pipeline, ({}, opts))
#   File "C:\Python\lib\site-packages\pyscaffold\actions.py", line 99, in invoke
#     return action(*struct_and_opts)
#   File "C:\Python\lib\site-packages\pyscaffold\actions.py", line 222, in get_default_options
#     info.check_git()
#   File "C:\Python\lib\site-packages\pyscaffold\info.py", line 126, in check_git
#     raise GitNotInstalled
# pyscaffold.exceptions.GitNotInstalled: Make sure git is installed and working. Use flag --very-verbose for more information.

[AaronCanty]

Excellent! Will save future headaches :)