toolbox: X11 applications no longer work with GNOME 3.38

Describe the bug

In Fedora 33, graphical applications no longer work from within toolbox containers when in Wayland. This breaks workflows for everyone using Silverblue and is relying on toolbox where graphical applications are needed. (Mainly: development work which may require graphical tools like gitk, VS Code, and so on.)

Steps how to reproduce the behaviour

1. Use Wayland, not X
2. Start a toolbox container
3. Run a graphical app, such as gitk
4. See an error where it cannot connect to X

Expected behaviour Graphical apps should show up.

Actual behaviour

When running gitk from within toolbox, the following happens:

$ gitk
application-specific initialization failed: couldn't connect to display ":0"
Error in startup script: couldn't connect to display ":0"
    while executing
"load /usr/lib64/libtk8.6.so Tk"
    ("package ifneeded Tk 8.6.10" script)
    invoked from within
"package require Tk"
    (file "/usr/bin/gitk" line 10)

Output of toolbox --version (v0.0.90+)

toolbox version 0.0.95

Toolbox package info (rpm -q toolbox)

toolbox-0.0.95-1.fc33.x86_64

Output of podman version

Version:      2.1.0-dev
API Version:  1
Go Version:   go1.15
Built:        Tue Aug 25 14:48:48 2020
OS/Arch:      linux/amd64

Podman package info (rpm -q podman)

podman-2.1.0-0.179.dev.git43f2771.fc33.x86_64

Info about your OS Fedora Silverblue 33 beta

Additional context

This worked fine in the 2020-09-14 build of Silverblue 33 beta. It broke somewhere between then and the latest build of 2020-09-20. I believe it is podman related, especially due to it being a dev build.

Did a development version of podman slip into F33/SB, breaking toolbox, again?

…Or is it intended to use podman 2.1.x in Fedora 33 (and therefore toolbox would have to workaround or add support for the new version)?

Discussed in https://discussion.fedoraproject.org/t/issues-with-some-graphical-apps-in-f33-containers-toolbox/23456.