Update setup-env to set XDG_DATA_DIRS for old systems

[mvk]

resolve #80

[mvk]

@alexmurray , please comment, and hopefully merge 🙏

[alexmurray]

Thanks - I've retargetted this to the master branch which is where stable builds of the snap come from.

[mvk]

Thanks - I've retargetted this to the master branch which is where stable builds of the snap come from.

Thank you, @alexmurray , the issue is not in master nor in pgtk,
It is only for the emacs-29 branch.

[alexmurray]

The emacs-29 branch is not used anymore - as you can see at https://launchpad.net/~alexmurray/+snap/emacs the master branch gets published to the beta channel in the store and then I manually promote that to stable. So if this is not needed on master (ie if the current stable emacs snap does not need this change) then this PR should be closed.