It seems that deploy workflow is broken for a few days now.
This is due to an issue with a newer version of Pulumi that removes a flag (-root) that got into ubuntu-latest github runner image.
More info and workarounds described in here: anomalyco/sst#6314

I would be glad to contribute a fix but I'm sadly not very familiar with SST's use and paths it uses so I prefer letting someone more capable of writing the fix.