Fix for diff when run from non-git root directory

[turculaurentiu91]

The problem

As observed in the issue #361, when you run pint with --diff=[branch] from an inner directory (non-git root directory) it affects 0 files..

The cause is the different behaviour between git status and git diff. Let's take a laravel project, that is stored in the project folder of a git repository. So the composer file is in project/composer.json

When git status is run from the dirty method it returns a relative path to the changed files, starting from the current directory.
Running git status --short -- '**.php*' from the project directory, will output routes/web.php

pint/app/Repositories/GitPathsRepository.php

Line 35 in 6f113c1

$process = tap(new Process(['git', 'status', '--short', '--', '**.php']))->run();

When git diff is run from the diff method it returns a full path starting from the git root directory. so running git diff --name-only --diff-filter=AM main..HEAD -- '**.php' from the project directory, will output project/routes/web.php

pint/app/Repositories/GitPathsRepository.php

Lines 55 to 60 in 6f113c1

	$files = [
	'committed' => tap(new Process(['git', 'diff', '--name-only', '--diff-filter=AM', "{$branch}...HEAD", '--', '**.php']))->run(),
	'staged' => tap(new Process(['git', 'diff', '--name-only', '--diff-filter=AM', '--cached', '--', '**.php']))->run(),
	'unstaged' => tap(new Process(['git', 'diff', '--name-only', '--diff-filter=AM', '--', '**.php']))->run(),
	'untracked' => tap(new Process(['git', 'ls-files', '--others', '--exclude-standard', '--', '**.php']))->run(),
	];

Later down the line, when we append the path to the output of any of those functions, in the processFileNames method, we append the path that already includes the project directory, causing the fully qualified path to become /home/laurentiu/git-root/project/project/routes/web.php

pint/app/Repositories/GitPathsRepository.php

Line 92 in 6f113c1

return $this->path.DIRECTORY_SEPARATOR.$file;

Proposed solution

My proposed solution is to only use the git diff command for both dirty and diff methods, then get the git root directory using git rev-parse --show-toplevel to find the fully qualified path to the git repository and append this instead.

I have not included any tests, as tests that runs git commands, that includes git repository are not that straight forward to write.

[turculaurentiu91]

Also note that the windows server 2019 runner was retired causing the CI checks to fail actions/runner-images#12045

[taylorotwell]

Pending review from @nunomaduro