libstdc++: Fix dumb typos in ALT128 support in <format> [PR107720]

This is only a partial fix for the PR.

libstdc++-v3/ChangeLog:

	PR libstdc++/107720
	* include/std/format (__format::_Arg_t): Fix typo in enumerator
	name.
	(_Arg_value::_S_get): Fix missing semi-colons.
1 file changed