users' .gitconfig affects downloading test cases from Library-Checker

[kmyk]

Description

We invoke generate.py at https://github.com/yosupo06/library-checker-problems to generate test cases of problems in Library-Checker, and use git command to checkout this repository.
For example, core.autoCRLF=true causes a problem (yosupo06/library-checker-problems#598).

Detecting core.autoCRLF=true config or CRLF in sample files and show warnings on oj command or generate.py?

Error log

yosupo06/library-checker-problems#598 (comment)

Other notes

• It seems git has no option to ignore .gitconfig like vim's -u NONE. Unsetting or making empty $HOME may work. However, .gitconfig has other fields which we shouldn't disable, e.g. http.proxy
• Should this be solved in https://github.com/yosupo06/library-checker-problems?
• cc @yosupo06