uucore: change sig of detect_system_locale to remove unsafe env::set_var

[oech3]

coreutils/src/uucore/src/lib/mods/locale.rs

Lines 416 to 417 in 0b04f5e

	fn detect_system_locale() -> Result<LanguageIdentifier, LocalizationError> {
	let locale_str = std::env::var("LANG")

This requires many unsafes. Sub issue of #12238 .