Bug#944515: reportbug: Cannot use UI gtk because of "please install..." but they are installed

[Fabrice BAUZAC <noon@mykolab.com>]

Package: reportbug
Version: 7.5.3
Severity: important

Dear Maintainer,

On my machine, reportbug refuses to use the GTK UI:

  $ reportbug --ui=gtk
  Cannot use UI gtk because of "Please install the python3-gi and
  gir1.2-gtk-3.0 packages to use this interface.", defaulting to
  "text"

The mentioned packages are installed though:

  $ dpkg-query -W python3-gi gir1.2-gtk-3.0
  gir1.2-gtk-3.0:amd64 3.24.12-1
  python3-gi           3.34.0-1

Why doesn't it use the GTK UI?

-- Package-specific info:
** Environment settings:
EDITOR="emacsclient"
PAGER="cat"
EMAIL="noon@mykolab.com"
NAME="Fabrice BAUZAC"
INTERFACE="text"

** /home/noon/.reportbugrc:
reportbug_version "7.5.3"
mode standard
ui text
realname "Fabrice BAUZAC"
email "noon@mykolab.com"
smtphost "smtp.kolabnow.com:587"
smtpuser "noon@mykolab.com"
smtppasswd <omitted>
smtptls

-- System Information:
Debian Release: bullseye/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 5.2.0-3-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=ANSI_X3.4-1968) (ignored: LC_ALL set to C), LANGUAGE=en_US:en (charmap=ANSI_X3.4-1968) (ignored: LC_ALL set to C)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages reportbug depends on:
ii  apt                1.8.4
ii  python3            3.7.5-1
ii  python3-reportbug  7.5.3
ii  sensible-utils     0.0.12

reportbug recommends no packages.

Versions of packages reportbug suggests:
pn  claws-mail                                 <none>
pn  debconf-utils                              <none>
pn  debsums                                    <none>
pn  dlocate                                    <none>
ii  emacs-bin-common                           1:26.1+1-4
ii  exim4-daemon-light [mail-transport-agent]  4.92.3-1
ii  file                                       1:5.37-6
ii  gnupg                                      2.2.17-3
pn  python3-urwid                              <none>
pn  reportbug-gtk                              <none>
ii  xdg-utils                                  1.1.3-1

Versions of packages python3-reportbug depends on:
ii  apt                1.8.4
ii  file               1:5.37-6
ii  python3            3.7.5-1
ii  python3-apt        1.8.4
ii  python3-debian     0.1.36
ii  python3-debianbts  2.8.2
ii  python3-requests   2.21.0-1
ii  sensible-utils     0.0.12

python3-reportbug suggests no packages.

-- no debconf information