Don't depend on en_US locale to be installed

[stefanhaller]

For some of the git commands that lazygit uses, it needs to force the language to English because it parses git's output and needs to react to certain things. It used to do this by setting the locale to en_US.UTF-8; some users reported that this locale isn't available on their systems. Use the "C" locale instead, which achieves the same result and is guaranteed to be available everywhere.

Fixes #4731.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for c31b6041	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (c31b604)	Report Missing	Report Missing	Report Missing
Head commit (99a83ef)	58234	50648	86.97%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#4949)	7	7	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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