gitoxide: CommandForbiddenInModulesConfiguration Bypass in gix_submodule::File::update() Enables Arbitrary Command Execution via .gitmodules

Summary gixsubmodule::File::update is the API that gates whether an attacker-supplied .gitmodules file may set update = !. The function is designed to return ErrCommandForbiddenInModulesConfiguration unless the !command value came from a trusted local source .git/config. Git CVE CVE-2019-19604...