Fix infinite recursion on Windows

[ibachar-es]

On windows, when running using VSCode and using the integrated terminal to launch my application, _caller_path returns a path starting with c:\ (lowercase) while os.path.abspath(os.sep) return C:\ (uppercase). This causes infinite recursion in _find_file

[henriquebastos]

Can you please provide a test case?

[sourcery-ai]

Sourcery Code Quality Report

✅  Merging this PR will increase code quality in the affected files by 0.19%.

Quality metrics	Before	After	Change
Complexity	1.86 ⭐	1.81 ⭐	-0.05 👍
Method Length	40.66 ⭐	41.12 ⭐	0.46 👎
Working memory	5.46 ⭐	5.39 ⭐	-0.07 👍
Quality	84.47% ⭐	84.66% ⭐	0.19% 👍

Other metrics	Before	After	Change
Lines	296	304	8

Changed files	Quality Before	Quality After	Quality Change
decouple.py	82.34% ⭐	82.22% ⭐	-0.12% 👎
tests/test_autoconfig.py	88.93% ⭐	89.34% ⭐	0.41% 👍

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
decouple.py	RepositoryEnv.__init__	10 🙂	114 🙂	11 😞	55.54% 🙂	Extract out complex expressions
decouple.py	Config.get	7 ⭐	81 🙂	11 😞	62.91% 🙂	Extract out complex expressions
decouple.py	Csv.__init__	0 ⭐	42 ⭐	10 😞	77.78% ⭐	Extract out complex expressions

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[ibachar-es]

@henriquebastos Done

[ibachar-es]

@henriquebastos It seems Sourcery complains about lines of code I didn't change in this PR