Tag: Fix error message display on tag creation

The error message was displayed using information dialog. As a result,
it is displaying git-cola icon instead of error icon.

This change use the proper error dialog instead of information dialog.

Reported-by: Ｖ字龍(Vdragon) <pika1021@gmail.com>
Signed-off-by: Minarto Margoliono <lie.r.min.g@gmail.com>