t9138-git-svn-authors-prog.sh fixups

t9138-git-svn-authors-prog.sh fixups

Several fixups of the t9138-git-svn-authors-prog.sh test script to
follow current recommendations in t/README.

  - Fixed a Perl script with a full "#!/usr/bin/perl" shebang
    to use write_script() and $PERL_PATH as per t/README.

  - Placed svn-authors data setup inside a test_expect_success.

  - Fixed trailing quotes to use the same indentation throughout.

Signed-off-by: Jeremiah Mahler <jmmahler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>