Don't use unicode literals for git_multimail
    
    It uses a literal as a type() argument, which doesn't work with unicode.
    This is also a file we forked from upstream, so we shouldn't be changing
    it up.
    This could perhaps break python3 compatibility, but we should just either
    work with upstream to fix that, or rebase on the latest upstream if they
    already have.
    
    Fixes: #3884
    Signed-off-by: Patrick Uiterwijk <patrick@puiterwijk.org>