[rubygems/rubygems] Rework bundle gem specs so that they work on Wi…

…ndows

Most of the commands run by these specs actually prompt for user input
but for some reason `Open3` outside of Windows ignores that and goes on
with no user input. Windows does not like this.

This commit refactors these specs so that:

* They don't prompt for user input when not necessary.
* They pass proper user input when necessary.

As long as no user input is needed, most specs pass, so it allows to
remove the `:readline` tag from most of them.

rubygems/rubygems@3dfabcdae4