Additional drivers tab cause uncancellable operation that prevents the program from closing

[Nathan Teodosio]

Start software-properties-gtk, switch to additional drivers tab. The program will start consuming 100% CPU for quite some time (many seconds or minutes depending on the machine).

There is however no way to cancel the operation other than killing software-properties. Trying to close the window or clicking Close button hangs.

Test plans
----------

1. Start software-properties-gtk
1.1. Go to additional drivers tab.
1.2. Click close at the south-east corner or close the window via your window manager.
Expected. Window closes immediately.

4. Start software-properties-gtk
4.1. Go to additional drivers tab and wait.
Expected: The viewport will at the end say that either no drivers are available or show a list of drivers such as in the drivers-list.png attachment. The cancel/retry buttons are gone in the latter case.

2. Start software-properties-gtk and 'top' in a terminal
2.1. Go to additional drivers tab.
Expected: The 'python3' command starts consuming 100% CPU.
2.2. Click cancel.
Expected: The aforementioned process is no longer hogging the CPU, indicating that the driver scan really stopped. The button is now retry, clickable.
2.3. Click retry.
Expected: The 'python3' command starts consuming 100% CPU. The button is now cancel.

3. Start software-properties-gtk and 'top' in a terminal
3.1. Go to additional drivers tab.
3.2. Get the PID of the 'python3' process consuming 100% CPU and kill it with kill -29 PID
Expected: The viewport reports the error. Retry is clickable.

5. Start software-properties-gtk
5.1. Introduce a unconditional exception in /usr/lib/python3/dist-packages/UbuntuDrivers/detect.py:system_device_drivers, e.g.:
--->
--- /usr/lib/python3/dist-packages/UbuntuDrivers/detect.py
+++ /usr/lib/python3/dist-packages/UbuntuDrivers/detect.py
@@ -866,4 +866,5 @@

 def system_device_drivers(apt_cache=None, sys_path=None, freeonly=False):
+print(fooo)
     '''Get by-device driver packages that are available for the system.

<---
5.2. Go to additional drivers tab.
Expected: "An error occurred while searching for drivers."; In the terminal, the backtrace is shown:
--->
Traceback (most recent call last):
  File "/home/nteodosio/canonical/ubuntu-pro/software-properties/softwareproperties/gtk/SoftwarePropertiesGtk.py", line 1456, in detect_drivers
    raise(self.p.exception)
Exception: Traceback (most recent call last):
  File "/home/nteodosio/canonical/ubuntu-pro/software-properties/softwareproperties/gtk/SoftwarePropertiesGtk.py", line 121, in run
    multiprocessing.Process.run(self)
  File "/usr/lib/python3.12/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/home/nteodosio/canonical/ubuntu-pro/software-properties/softwareproperties/gtk/SoftwarePropertiesGtk.py", line 1437, in wrapper_system_device_drivers
    devices = detect.system_device_drivers(cache)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/UbuntuDrivers/detect.py", line 919, in system_device_drivers
    print(fooooo)
          ^^^^^^
NameError: name 'fooooo' is not defined
<---