git: workaround occasional -watch error message
    
    I'm not sure how this happens (perl 5.34.1 on FreeBSD 13.2)
    but it appears the {sock} check can succeed and then go undef
    and become unable to call ->owner_pid.
    
    This happens when libgit2 is in use, so perhaps that's a factor.
    In any case, the rest of the tests succeed.