git-svn: avoid segfaults in 'git svn branch'
    
    Re-enable t9128, t9141, and t9167 which were disabled due to these
    random segfaults.  The bug has also been reported against the subversion
    perl bindings in Debian¹.  Hopefully this will reach upstream subversion
    if a fix is made to subversion.
    
    ¹ https://bugs.debian.org/888791