Singularity <3.6 can't pull containers created with Singularity >=3.9

[PhMueller]

Basically the title.

The github actions fail when github tries to download a container (singularity pull ...) from the registry that was created using a newer singularity version.
This happened to me while working with the yahpo gym container.

On my local computer, i am using singularity 3.9.3.
Github runs 3.5.3

Interestingly, I also can't install an older version of singularity as described in the github actions install script. That fails due to a "file not found error".
Maybe they use a cached version.

This results in two tasks:

• Update the github actions script to support installing "old singularity" versions
• Find a way to create containers with singularity >3.9.3 so that it is compatible with older singularity versions