Provide more linux binaries

First and foremost consider this:

• Only RetroArch bugs should be filed here. Not core bugs or game bugs
• This is not a forum or a help section, this is strictly developer oriented

Description

(btw) how do I get rights in IRC? Haven’t found a clue anywhere. Cannot message…

For most platforms, multiple versions (current, old, nightly) are provided.
For linux, only the current version is provided.
Because of https://github.com/libretro/RetroArch/issues/12262, I wanted to go back to 1.9.0.
However, the Ubuntu PPA's 1.9.0 is actually a 1.9.1 in disgues (yep, it says 1.9.0, but --version gives 1.9.1),
the snap store has no "previous" channel, app iamges are not available for older version (only current stable).
Haven’t checked flatpacks.

Expected behavior

For e.g. windows, you have URLs like this:

• https://buildbot.libretro.com/stable/1.9.1/windows/x86_64/RetroArch-Win64-setup.exe

Also, multiple nightlies are availble:

• https://buildbot.libretro.com/nightly/windows/x86_64/

Actual behavior

The linux URLs do not include a version:

• https://flathub.org/repo/appstream/org.libretro.RetroArch.flatpakref
• http://buildbot.libretro.com/nightly/linux/x86_64/RetroArch_Qt.7z

Using linux nightlies:

• https://buildbot.libretro.com/nightly/linux/x86_64/
  … but they do not go back enought in time

Snapstore has no "old" channel:

name:      retroarch
summary:   RetroArch
publisher: hunterk (libretro)
store-url: https://snapcraft.io/retroarch
contact:   https://forums.libretro.com/
license:   GPL-3.0
[…]
snap-id:      7xMPaiM3yBx0npSKPNuTYNhzW4xI9CDk
tracking:     latest/stable
refresh-date: today at 08:40 CEST
channels:
  latest/stable:    1.9.1 2021-04-08 (453) 299MB -
  latest/candidate: 1.9.1 2021-04-08 (453) 299MB -
  latest/beta:      1.9.1 2021-04-08 (453) 299MB -
  latest/edge:      1.9.1 2021-04-12 (461) 299MB -
installed:          1.9.1            (453) 299MB -

Bisect Results

[n/a]

Version/Commit

m/a

Environment information

• OS: linux, any
• Compiler: [does not apply]

Start by tracing how the Linux artifacts linked in the issue are produced and published, including the stable and nightly buildbot paths, PPA, Snap, and Flatpak channels. Determine which packaging or release entry points control versioned and historical binaries; done means older Linux versions can be retrieved through documented versioned artifacts or channels.