Cannot connect using default bridges in 6.5

Multiple users already reported that since we released 6.5 yesterday.

In the logs I see:

Jul 17 09:38:30 amnesia tca[7099]: Traceback (most recent call last):
Jul 17 09:38:30 amnesia tca[7099]:   File "/usr/lib/python3/dist-packages/tca/ui/asyncutils.py", line 192, in wrapped_fn
Jul 17 09:38:30 amnesia tca[7099]:     ret = first()
Jul 17 09:38:30 amnesia tca[7099]:           ^^^^^^^
Jul 17 09:38:30 amnesia tca[7099]:   File "/usr/lib/python3/dist-packages/tca/ui/main_window.py", line 515, in do_tor_connect_config
Jul 17 09:38:30 amnesia tca[7099]:     self.app.configurator.tor_connection_config.enable_default_bridges(
Jul 17 09:38:30 amnesia tca[7099]:   File "/usr/lib/python3/dist-packages/tca/torutils.py", line 360, in enable_default_bridges
Jul 17 09:38:30 amnesia tca[7099]:     self.enable_bridges(bridges)
Jul 17 09:38:30 amnesia tca[7099]:   File "/usr/lib/python3/dist-packages/tca/torutils.py", line 348, in enable_bridges
Jul 17 09:38:30 amnesia tca[7099]:     raise ValueError("Can't set empty bridge list")
Jul 17 09:38:30 amnesia tca[7099]: ValueError: Can't set empty bridge list

And indeed, /usr/share/tails/tca/default_bridges.txt is empty.

To Do

• Ensure this does not happen again: empty list of default bridges should make us FTBFS
• Adjust our code that extracts the list of default bridges from the Tor Browser config (config/chroot_local-hooks/10-tbb)