software-properties-gtk crashed with AttributeError in run(): 'SoftwarePropertiesGtk' object has no attribute 'on_keyboard_Interrupt'

[Norbert]

Steps to reproduce:
1. Open terminal and execute `software-properties-gtk`
2. Wait it to open
3. Press <Ctrl>+<C> in the terminal to stop it.

Expected result:
* Software & Updates window closed quietly and clean

Actual results:
* Software & Updates window closed with errors in terminal

focal@focal-VirtualBox:~$ software-properties-gtk
^CTraceback (most recent call last):
  File "/usr/lib/python3/dist-packages/softwareproperties/gtk/SimpleGtkbuilderApp.py", line 54, in run
    Gtk.Application.run(self, None)
  File "/usr/lib/python3/dist-packages/gi/overrides/Gio.py", line 44, in run
    return Gio.Application.run(self, *args, **kwargs)
  File "/usr/lib/python3.7/contextlib.py", line 119, in __exit__
    next(self.gen)
  File "/usr/lib/python3/dist-packages/gi/_ossighelper.py", line 251, in register_sigint_fallback
    signal.default_int_handler(signal.SIGINT, None)
KeyboardInterrupt

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/bin/software-properties-gtk", line 101, in <module>
    app.run()
  File "/usr/lib/python3/dist-packages/softwareproperties/gtk/SimpleGtkbuilderApp.py", line 56, in run
    self.on_keyboard_Interrupt()
AttributeError: 'SoftwarePropertiesGtk' object has no attribute 'on_keyboard_Interrupt'
focal@focal-VirtualBox:~$

 and "Crash report" dialog afterwards.

ProblemType: Crash
DistroRelease: Ubuntu 20.04
Package: software-properties-gtk 0.98.6
ProcVersionSignature: Ubuntu 5.4.0-9.12-generic 5.4.3
Uname: Linux 5.4.0-9-generic x86_64
ApportVersion: 2.20.11-0ubuntu15
Architecture: amd64
CrashCounter: 1
CurrentDesktop: MATE
Date: Sun Jan 19 13:10:46 2020
ExecutablePath: /usr/bin/software-properties-gtk
InstallationDate: Installed on 2020-01-16 (2 days ago)
InstallationMedia: Ubuntu-MATE 20.04 LTS "Focal Fossa" - Alpha amd64 (20200115)
InterpreterPath: /usr/bin/python3.7
PackageArchitecture: all
ProcCmdline: /usr/bin/python3 /usr/bin/software-properties-gtk
Python3Details: /usr/bin/python3.7, Python 3.7.6, python3-minimal, 3.7.5-1ubuntu1
PythonArgs: ['/usr/bin/software-properties-gtk']
PythonDetails: /usr/bin/python2.7, Python 2.7.17, python-minimal, 2.7.17-1
SourcePackage: software-properties
Title: software-properties-gtk crashed with AttributeError in run(): 'SoftwarePropertiesGtk' object has no attribute 'on_keyboard_Interrupt'
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin lxd plugdev sambashare sudo