Accept environment variables with different cases on Windows. Fixes #607

[fabioz]

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[int19h]

I don't think that's the right way to fix the problem. This particular snippet, and the corresponding test case, was there for microsoft/ptvsd#2055 - and the underlying issue was exactly that, that variables will overwrite each other regardless of name case. So if debugpy gets a mismatched dict, when merging that with pre-existing environment variables, which one wins is essentially random on older Python versions (where dicts are unordered). So the user would silently get the wrong PATH with no clear indication as to why. The normalization & check prevents that by making the issue explicit.

I believe this is consistent with what Windows does. It doesn't actually allow you to have two variables in the same environment that differ only by case when spawning a new process. So the client shouldn't be able to specify a dict with two variables that differ only by case - it's ambiguous which value wins in that case. The client, when it generates the dict from environment, should be similarly case-insensitive on Windows.

[fabioz]

Humm, in this particular issue (#607) the user has Path and PATH with the same contents actually, so, maybe we can just check for that particular case and accept it if both map to the same value (so, it wouldn't matter who wins as they're effectively the same).

[int19h]

That sounds reasonable.

[sonarcloud]

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