Re: t7528-signed-commit-ssh.sh fails due to ssh-agent fails to start with ENAMETOOLONG

> But looking at this test, there's something even more funky going on.
> Our $HOME will always have a space in it, because no matter where you
> set the root, we will create "trash directory.t7582..." to work in. But
> AFAICT, ssh-agent does not quote the path in its output. So for example:
> 
>   d='/tmp/has spaces'
>   mkdir "$d"
>   HOME=$d ssh-agent
> 
> will produce:
> 
>   SSH_AUTH_SOCK=/tmp/has spaces/.ssh/agent/s.IcPuGe26YY.agent.6PtD3uhM4O; export SSH_AUTH_SOCK;
> 
> which is nonsense to eval. And indeed, the "working" version of this
> test (without a really long root path) produces:
> 
>   ./t7528-signed-commit-ssh.sh: 1: eval: directory.t7528-signed-commit-ssh/.ssh/agent/s.IcPuGe26YY.agent.sOzoazWiDc: not found
> 
> I expected that would cause ssh-add to fail, since our SSH_AUTH_SOCK
> would point to truncated garbage, and we can't talk to the agent. But it
> doesn't even do that. The extra space turns that line from a variable
> assignment into a one-shot variable attached to a command that fails to
> run. And so we're left with the original SSH_AUTH_SOCK from the
> environment, the one in my real $HOME outside of the trash directory.
> Yikes!
> 
> If I unset SSH_AUTH_SOCK in my environment, then the test consistently
> fails. But I'm somewhat amazed that nobody has complained about this
> before. Surely somebody somewhere (especially CI!) is running t7528
> without SSH_AUTH_SOCK set in the environment. Which makes wonder if I'm
> missing something.