web app: add tests for insecure symlinks that should return 403
web app: add tests for insecure symlinks that should return 403

Signed-off-by: Stefano Zacchiroli <d7cdf09fc0f0426e98c9978ee42da5d61fa54986@upsilon.cc>

sophiejjj/debsources,clemux/debsources,devoxel/debsources,sophiejjj/debsources,oorestisime/debsources,matthieucan/debsources,Debian/debsources,Debian/debsources,clemux/debsources,matthieucan/debsources,devoxel/debsources,zacchiro/debsources,oorestisime/debsources,vivekanand1101/debsources,oorestisime/debsources,vivekanand1101/debsources,sophiejjj/debsources,oorestisime/debsources,devoxel/debsources,matthieucan/debsources,clemux/debsources,oorestisime/debsources,Debian/debsources,Debian/debsources,devoxel/debsources,zacchiro/debsources,sophiejjj/debsources,matthieucan/debsources,clemux/debsources,zacchiro/debsources,devoxel/debsources,Debian/debsources,matthieucan/debsources,vivekanand1101/debsources,vivekanand1101/debsources,clemux/debsources,vivekanand1101/debsources,zacchiro/debsources,sophiejjj/debsources,zacchiro/debsources