add polkitbackendjsauthoritytest-wrapper.py into release tarball

I got polkit-0.117 release tarball at https://www.freedesktop.org/software/polkit/releases/polkit-0.117.tar.gz. Unfortunately make check fails for it because a script polkitbackendjsauthoritytest-wrapper.py is missing.

Add it into polkitbackendjsauthoritytest_SOURCES so that autotools will add it into the release tarball created with make dist-gzip.