Changes

ttcn3-gbproxy-test-fr: don't use old libosmocore

Fix that we are currently building osmo-gbproxy against an old
libosmocore in ttcn3-gbproxy-test-fr. This is currently causing the job
to fail with:

  /usr/bin/ld: gb_proxy_vty.o: in function `log_set_bvc_filter':
  /tmp/osmo-gbproxy/src/gb_proxy_vty.c:477: undefined reference to `log_set_filter'
  /usr/bin/ld: /tmp/osmo-gbproxy/src/gb_proxy_vty.c:478: undefined reference to `log_set_filter_data'
  collect2: error: ld returned 1 exit status

Related: libosmocore Ie48e7e635feb91509b9c034394df4fb16cb931a3
Change-Id: I15fcb4fd1f145bd913456ac08356e9fa65e34269